Fix 'My PC is slow all of a sudden' — the order of attack

Steps

1. 01

   Check whether the disk is pegged at 100%

   • Press Ctrl+Shift+Esc to open Task Manager — if it opens as a small window, click 'More details' in the bottom-left
   • Click the Performance tab (left side on Windows 11, top row on Windows 10), then click Disk
   • Watch the usage percentage for a minute while you do something normal — pinned at or near 100% is your answer

   ✓You should see: A disk graph whose usage stays near 100% even when you're only browsing.

   Why?

   'Pegged' means the drive is working flat-out with nothing to spare, so every app queues behind it — on a mechanical hard drive this is often the whole story, and an SSD pinned at 100% for minutes may be failing.

   Also see: Run a disk health check before it's too late

2. 02

   Find any app eating CPU or memory

   • Click the Processes tab — Task Manager is still open from the disk check
   • Click the CPU column header to sort by it and scan for anything pinned high, then click the Memory column header and do the same pass again
   • Right-click a suspect → 'Open file location' to see what it actually is before you end it

   Why?

   Windows deliberately fills spare memory with cache and hands it back on demand, so a high percentage alone isn't a fault — the tell is one nameable app pinned high while the rest of the PC waits.

   Also see: Hunt down memory hogs

3. 03

   Check what Windows Update installed last night — and undo it

   • Settings›Windows Update›Update history(Windows 10:Settings›Update & Security›Windows Update›View update history)
   • Look for updates in the last few days — driver entries mentioning your graphics card, chipset or storage are the ones to suspect
   • To remove a bad Windows update: Settings → Windows Update → Update history → Uninstall updates under Related settings (Windows 10:Settings›Update & Security›Windows Update›View update history›Uninstall updates)
   • To roll back a bad driver:Device Manager›the device›Properties›Driver tab›Roll Back Driver— if that button is greyed out, no previous version is stored and this route is closed

   Why?

   Driver updates install silently overnight; a bad GPU or storage driver is a classic cause of sudden slowness that closing apps will not fix.

   Also see: Screen flickering on Windows: driver, cable or refresh rate

4. 04

   Repair corrupted system files with DISM, then sfc

   • Press the Windows key, type 'cmd',right-click Command Prompt›Run as administrator— when Windows asks 'Do you want to allow this app to make changes?', click Yes; a normal window will refuse the repair
   • Run DISM /Online /Cleanup-Image /RestoreHealth first and let it finish — a progress bar that pauses is normal
   • Then type sfc /scannow and press Enter, and leave it alone for 5–15 minutes
   • If sfc still reports corrupt files it couldn't fix, restart and run it once more

   ✓You should see: 'Windows Resource Protection found violating files and successfully repaired them', or 'did not find any integrity violations'. 'Found corrupt files but was unable to fix some' after both commands is the cue to run a disk health check.

   Why?

   This is Microsoft's documented order. sfc replaces corrupted system files from known-good copies held in the local component store; DISM repairs that store first, so sfc has clean parts to work with — run the other way round, sfc can keep reporting files it can't fix. Corruption shows up as random slowness rather than crashes, which is why it earns a place here.