When Windows becomes slow, crashes or refuses to update, the cause is often quiet corruption of system files. Before installing a “PC optimiser”, use the two repair tools that ship with every copy of Windows: DISM (Deployment Image Servicing and Management) and SFC (System File Checker).
Before you start
- An administrator account on the PC
- An internet connection – DISM downloads clean files from Windows Update
- 30–45 minutes, and your work saved
Step 1 – Open an elevated Command Prompt
- Open Start and type cmd.
- Right-click Command Prompt and choose Run as administrator.
- Confirm the window title reads Administrator: Command Prompt.
Step 2 – Repair the Windows image with DISM
SFC repairs files by copying them from the Windows component store. If that store is damaged, SFC can’t fix anything – so repair the store first.
DISM /Online /Cleanup-Image /RestoreHealth- It usually takes 10–25 minutes.
- Progress can sit at 20 %, 40 % or 62 % for a while – that is normal; don’t close the window.
- Finish: The restore operation completed successfully.
Step 3 – Repair system files with SFC
sfc /scannow| Result | What it means |
|---|---|
| Did not find any integrity violations | System files are healthy. |
| Found corrupt files and successfully repaired them | Fixed – restart the PC. |
| Found corrupt files but was unable to fix some of them | Restart, run DISM again, then SFC once more. Details are in %windir%LogsCBSCBS.log. |
Step 4 – Restart and check
Restart the PC so repaired files are loaded. If performance is still poor, the cause is probably elsewhere – startup apps, a failing disk or low memory.
Do it in the right order
DISM first, SFC second. Running SFC on a damaged component store just reports errors it cannot repair.
Generate the commands for you
The Windows Repair Command Generator builds the right sequence for crashes, update failures, network problems or disk errors – for Command Prompt or PowerShell.
Frequently asked questions
How often should I run DISM and SFC?
Only when something is wrong – after crashes, failed updates or strange errors. There is no benefit to running them on a healthy PC.
Can I use the PC while they run?
Yes, but it will be slower. Avoid installing software or updates at the same time.
Is it safe?
Yes. Both tools only replace protected Windows files with verified copies; your documents and apps are not touched.
Written by
Inder Kochar
Systems & Network Engineer – I write up the fixes I use with clients, tested on real systems. Stuck on something similar?
