DISM and System File Checker are built-in repair tools for suspected Windows system-file problems. They are not routine speed boosters.
Prepare first
Save your work and back up important files. On a work device, get permission from IT. Ensure you have an administrator account and allow time for each command to finish.
Run Microsoft’s sequence
Search Start for Command Prompt and choose Run as administrator. Type DISM.exe /Online /Cleanup-image /Restorehealth and wait for completion. Then type sfc /scannow and wait until it reaches 100%.
Keep the result
Record the final message and restart if prompted. If the repair fails or says it could not fix files, save the exact output for a technician rather than repeatedly running commands without a plan.
Further reading: Microsoft Support: System File Checker.