How to fix a slow computer: diagnose it by symptom, then fix the cause

Start here: which kind of slow is it?

Before anything else, close the apps and browser tabs you are not using, and restart if that does not help. Microsoft's own list of fixes ends with exactly that, because many open apps and tabs slow a PC by themselves. If the slowness comes back, note when it happens and match it here:

Task Manager is the first tool for almost every row. Press Ctrl + Shift + Esc, or right-click Start and select Task Manager. On the Processes page, select a column header such as CPU, Memory or Disk to sort by it, highest first: the process at the top is the one using that resource now. The Performance page draws each resource over time.

Judge what you see over minutes, not seconds. Microsoft's guidance on high CPU usage calls short spikes normal and treats usage that stays at 80 percent or higher for extended periods as the problem worth chasing. For an average over time instead of a snapshot, open Resource Monitor (type resmon in Start, or run perfmon /res) and, on its CPU tab, sort by Average CPU.

Slow to start up, or slow right after you sign in

Slow start-up has two shapes: the PC takes a long time to reach the desktop, or it gets there quickly and then stays sluggish for the first few minutes. Either way, check the apps that start with Windows first. Microsoft notes that they affect both how fast the device starts and how the system performs afterwards.

1. Open Task Manager and select Startup apps. The Startup impact column rates each app from what it cost at start-up: High means more than 1 second of processor time or more than 3 MB of disk activity.
2. Select each High-impact app you do not need the moment you sign in, and select Disable. It stops starting automatically; you can still open it yourself.
3. Restart and compare.

The same list, with a switch per app, is in Settings > Apps > Startup. An app missing from both may start from a startup folder instead: press Windows + R, type shell:startup and delete its shortcut there. Our optimization guide has the full impact table and what is usually safe to switch off.

Find a cause that is not on the list: clean boot

Windows services do not appear in the startup apps list. If disabling startup apps does not help, a clean boot starts Windows with only essential drivers and startup programs, which shows whether third-party software is the cause at all:

1. Sign in as an administrator, type msconfig in Start and open System Configuration.
2. On the Services tab, select Hide all Microsoft services, then Disable all, then Apply.
3. On the Startup tab, select Open Task Manager and disable every enabled startup app, noting which ones you changed.
4. Restart. If the PC is now quick, one of the disabled items is the cause: re-enable the upper half of the services, restart, and keep halving until you find it, then do the same with the startup apps.
5. When you are done, choose Normal startup on the General tab and re-enable what you disabled.

If start-up is slow and the PC also freezes now and then, check the drive's health (next section) before anything else.

Disk at 100%: find what is using it

When Task Manager's Disk column sits at or near 100%, the drive is overwhelmed: reads and writes queue behind each other, and every program that needs the disk waits its turn, which is why the whole PC seems to freeze. That is a different problem from a full drive, which shows in Settings > System > Storage and which Microsoft lists separately: low disk space can reduce performance too.

To confirm it and find the source:

1. In Task Manager > Processes, sort by Disk and note the top process. Short bursts are normal; a process that stays on top for many minutes is the one to deal with.
2. Measure how long the drive takes to answer. Microsoft's performance troubleshooting guide treats an average read or write time under 15 ms as healthy, above 25 ms as a warning and above 50 ms as critical, when it lasts a minute or more. In PowerShell, Get-Counter samples those counters every 5 seconds for a minute. The values are in seconds, so 0.015 is 15 ms:

Get-Counter -Counter '\PhysicalDisk(*)\Avg. Disk sec/Read','\PhysicalDisk(*)\Avg. Disk sec/Write' -SampleInterval 5 -MaxSamples 12

What the top process tells you:

• Windows Search indexing. The first full index can take up to a couple of hours; after that, it re-indexes only what changed. If indexing never settles, open Settings > Privacy & security > Search: Enhanced mode indexes the entire PC and may use more resources, while Classic covers Documents, Pictures, Music and the desktop.
• Your antivirus. A full scan checks every file and program on the device, so the disk stays busy until it finishes. Let it complete.
• Memory running short. If Task Manager also shows memory close to its limit (see the memory section), Windows is writing memory pages to the page file on disk. Fix the memory problem and the disk load drops with it.
• Nothing obvious. If no process explains the load, or the drive is slow even when little is running, check its health.

Check the drive's health

Windows 11 reads health data from NVMe solid-state drives. Go to Settings > System > Storage > Advanced storage settings > Disks & volumes, select the drive and choose Properties. Drive health shows the estimated remaining life, the available spare capacity and the temperature, and Windows raises a critical warning when spare capacity falls below the manufacturer's threshold, when media errors have degraded reliability, or when the drive has switched to read-only. Microsoft lists device slowness, freezing and longer start-up times among the symptoms. Windows monitors only NVMe drives this way, not SATA SSDs or hard disk drives.

For those, ask PowerShell, opened as administrator. Get-PhysicalDisk reports each drive's health status, and Get-StorageReliabilityCounter reads the counters a drive keeps about its temperature, errors, wear and hours in use:

Get-PhysicalDisk | Format-Table FriendlyName, HealthStatus, OperationalStatus
Get-PhysicalDisk | Get-StorageReliabilityCounter | Format-List Temperature, Wear, ReadErrorsUncorrected, WriteErrorsUncorrected, PowerOnHours

A blank field means the drive does not report that counter; even Microsoft's own example output leaves Wear empty. A health status other than Healthy, or uncorrected errors that keep growing, are reasons to back up now and plan a replacement.

One process keeps the processor busy

Sort Task Manager's Processes page by CPU. If one entry stays at the top while you are not using it, that is the process to deal with, and what you do depends on what it is:

• An app you recognize, such as a browser, a chat or sync client, or a game launcher: close it, update it, and if it keeps doing this, take it to the vendor, as Microsoft advises for third-party processes.
• Service Host (svchost.exe). One Service Host process can hold several Windows services. Expand the group in Task Manager to see which services are inside; Microsoft's procedure for a busy svchost starts by finding which of its services drives the usage.
• A name you do not recognize, especially one that comes back after you end it: scan for malware first (see the malware section).

For a program that is legitimately busy in the background, Task Manager's Efficiency mode helps. Microsoft describes it as limiting the resources a process uses by lowering its priority, so the apps in front of you stay responsive; our optimization guide shows where to switch it on.

Memory is full: commit charge and too many tabs

Memory trouble has its own pattern: the PC is fine with a few apps open and gets slower with every app or tab you add. To confirm it, open Task Manager > Performance > Memory and read Committed. It shows the commit charge, the memory Windows has promised to programs, against the commit limit, which is physical RAM plus the page file. Microsoft's introduction to the page file explains the stakes: when the commit charge reaches the limit, the system and programs may not get the memory they ask for, which can cause freezing and crashing.

• Committed stays well below the limit, even at your busiest: memory is not the bottleneck; look at the other rows of the table.
• Committed runs close to the limit: sort the Processes page by Memory, close what you do not need, and restart. If your normal workload reaches the limit, the lasting fixes are fewer programs at once or more RAM, not a bigger page file (the optimization guide explains why).

Browsers are the usual heavy user. Google's own advice is that Chrome works harder with every open tab, so close the tabs you are not using. Both major browsers can also put idle tabs to sleep:

• Chrome: Settings > Performance > Memory Saver deactivates tabs you are not using and reloads them when you return. Choose a level: Moderate, Balanced (recommended) or Maximum, which makes tabs inactive soonest.
• Microsoft Edge: sleeping tabs puts background tabs to sleep after two hours of inactivity by default; shorten the interval at edge://settings/system. Edge's performance detector also flags background tabs that use a lot of memory or processor time and offers to fix them.

Only the browser is slow

If other apps stay quick and only the browser crawls, first rule out the network: open the same page in a second browser. Microsoft's Edge troubleshooting guide uses the same test; if the page fails in the other browser too, the problem is the network or the website. If only one browser is slow, work through it in this order:

1. Find the heavy tab or extension. In Chrome, open More > More tools > Task Manager, sort by Memory, and end the tasks you no longer need; Google suggests looking for items labelled "Background page".
2. Test without extensions. Google's procedure: open the page in an Incognito window, and if it works there, turn off all extensions, then turn them back on one at a time until the problem returns, and remove that one. For Edge, Microsoft suggests uninstalling the extensions you do not need.
3. Update the browser. Chrome works best on the latest version, and in Edge, Settings > About Microsoft Edge applies any pending update.
4. Toggle graphics acceleration. Both browsers have a setting called Use graphics acceleration when available, which is on unless a policy turns it off (Edge, Chrome). Search for "acceleration" in the browser's settings. If scrolling and video stutter, turn it off, restart the browser and compare; turn it back on if it made no difference.
5. Reset or repair. Chrome's reset (Settings > Reset settings > Restore settings to their original defaults) returns the search engine, start-up and pinned tabs, site settings, cookies, and extensions and themes to their defaults, while keeping bookmarks and saved passwords. Edge can be repaired from Settings > Apps > Installed apps > Microsoft Edge > Modify > Repair, which Microsoft says should not affect your browser data and settings.

Only the network or Wi-Fi is slow

A PC that opens local files instantly but loads websites, downloads and video calls slowly has a network problem, not a computer problem. Confirm it the way Microsoft's Wi-Fi guide suggests: connect another device to the same Wi-Fi. If that one is slow too, the router or the internet connection is the issue, and the router may need maintenance or replacement.

If only this PC is slow:

1. Look for a process using the connection. In Task Manager, end processes that are using a lot of network bandwidth and that you do not need right now, such as a large download.
2. Check the signal. Move closer to the router, with fewer obstructions in between.
3. Run the troubleshooter. On Windows 11, the Network and Internet troubleshooter in the Get Help app runs diagnostics and tries to fix most problems by itself.
4. Stop the adapter saving power. If the connection keeps dropping, open Control Panel > Hardware and Sound > Power Options, select Change plan settings > Change advanced power settings, expand Wireless Adapter Settings and set Power Saving Mode to Maximum Performance. Changing the router's wireless channel can also reduce interference.
5. Restart the modem and router. This creates a new connection to your internet provider, and briefly disconnects everyone on the network.
6. Reset the network settings last. Network reset removes every network adapter and its settings, then reinstalls them with defaults after a restart, which is why Microsoft lists it as the last step to try.

Slow since an update or a new driver: find what changed

When a PC that was fine last week is slow now, look for what changed. Two built-in tools show what changed and when.

Reliability Monitor is the quicker one. Type "reliability" in Start and select View reliability history, or run perfmon /rel; Dell's guide walks through both routes. It draws one column per day. Along the top runs the System Stability Index, from 1 (least stable) to 10 (most stable), weighted towards recent failures. Below it, icons mark software installs and removals, including Windows updates and drivers, and failures of applications, Windows and hardware, kept for up to a year. Find the day the line dropped, select that column, and read what was installed that day and what failed after it.

Event Viewer holds the detail. Open it from Start, select the System or Application log (under Windows Logs), and open an event to read its description, as Microsoft's startup troubleshooting guide describes. Look at the errors and warnings from the time the slowness began; an error that repeats every few minutes is worth searching by its source and event ID.

Update history is the simplest list of all: Settings > Windows Update > Update history shows which updates were installed, and when (Windows Update FAQ).

Then undo the change that lines up with the slowdown:

1. A driver updated that day. Right-click Start, open Device Manager, expand the category, right-click the device and select Properties > Driver > Roll Back Driver, choose a reason and confirm. You need administrator rights, and Microsoft notes that when a problem starts after a Windows update, reinstalling the previous driver often resolves it.
2. A Windows update. Go to Settings > Windows Update > Update history > Uninstall updates, select the update and choose Uninstall. Not every update can be removed, and Microsoft does not recommend removing updates unless it is necessary, so treat this as a test: if the PC is quick again, install the next fixed update rather than staying unpatched.
3. A new version of Windows. After a feature upgrade, you can go back to the previous version for 10 days.
4. Several changes at once, or you cannot tell which: System Restore rolls back system files and settings but not personal files. On Windows 11 version 24H2 and later, point-in-time restore rolls the whole PC back to a recent automatic restore point, including apps, settings and personal files, so anything changed after that point is lost.

Slow when hot or on battery: throttling and power mode

Two things slow a healthy PC on purpose: heat, to protect the hardware, and power settings, to save energy.

Heat. Intel describes throttling as a mechanism that reduces the processor's clock speed when its temperature goes above its maximum (TjMax), both to protect the processor and to show that the system is overheating. The pattern to look for: a heavy task starts at full speed, then slows as the fans get loud and the case gets hot; in games it shows as stutter. Intel's checklist is the cooling: a fan that works, air that can get in and out, and a cooler fitted correctly with the right amount of thermal paste. On laptops the manufacturer sets the power limits, so its support tools and service are the place to take a laptop that throttles when clean.

Blocked vents and dusty fans are what a careful cleaning fixes. Our guide to cleaning computer hardware safely covers vents, fans and when to replace thermal paste.

Battery. Windows 11 keeps a separate power mode for Plugged in and On battery in Settings > System > Power & battery. Best power efficiency saves power by limiting background activity, and Energy saver turns on when the battery is low, dims the screen and limits background processes. A laptop that is quick on the charger and slow on battery is usually doing exactly what those settings ask. If you need the speed away from the charger, set On battery to Balanced or Best performance, and accept that the battery drains faster and the laptop may run warmer. If Power mode cannot be changed, a custom power plan is selected: choose Balanced in Control Panel > System and Security > Power Options. Our guide to extending laptop battery life covers the other side of that trade.

Slow because of malware or unwanted software

Malware can consume processor and disk resources, so a scan belongs on the list whenever the cause is not obvious, and first when an unfamiliar process is busy. Open Settings > Privacy & security > Windows Security > Virus & threat protection and run a Quick scan.

If it finds something, or the PC still seems wrong, run the Microsoft Defender Antivirus (offline scan) from Scan options. It restarts the PC and scans without loading Windows, where persistent malware has a harder time hiding or defending itself; the results appear afterwards under Protection history. For choosing protection beyond what Windows includes, see our guide to choosing antivirus software for your PC.

On a Mac: Activity Monitor

The same method works on a Mac with Activity Monitor. It lists processes with how much memory and CPU time each uses; click a column heading to sort. For memory, open the Memory pane and read the Memory Pressure graph: green means the Mac is using its RAM efficiently, yellow that it might eventually need more, and red that it needs more RAM. Apple also points out that free memory by itself does not make a Mac faster, because macOS performs best when it uses and manages all of its memory. The Energy, Disk and Network panes cover the other rows of the symptom table.

When none of this fixes it

If the PC does not start at all, or crashes with a stop code, that is a fault to troubleshoot rather than a slowdown. If it starts but stays slow after the steps above, Microsoft's recovery options for a PC that is slow, crashing or freezing run from least to most disruptive:

1. Run a troubleshooter: Settings > System > Troubleshoot > Other troubleshooters.
2. Reinstall Windows in place, which reinstalls the current version without affecting your files, apps or settings (Windows 11 version 22H2 and later).
3. Uninstall a recent update, or go back to the previous version within 10 days of an upgrade.
4. Point-in-time restore (Windows 11 version 24H2 and later).
5. Reset this PC, which reinstalls Windows from scratch and either keeps your personal files or removes everything.

Back up before you start: Microsoft warns that some recovery options can result in data loss.

Be realistic about age, too. Microsoft says that older PCs with outdated hardware may not see significant improvements from these steps, and that upgrading the device may then be the best long-term solution; our guide to upgrading a PC for better performance covers which part to change first, and when to replace the PC instead.

When slow PCs are a recurring ticket across a team, our IT support service traces recurring issues to their cause and fixes them at the root, patches operating systems and apps on a schedule, and advises on what to replace and when. Remote sessions happen only with your consent.