A-How-To: System File Checker (SFC) to fix Corrupted Files in Windows XP/Vista/7...

System File Checker (SFC) - scannow

SFC gives an administrator the ability to scan all protected files to verify their versions and it will attempt to replace missing or corrupted system files by proper versions if it can locate a valid copy on your hard disk. If it cannot find a copy on your hard disk it will ask you to insert your Windows XP CD. You must have a valid copy of your Windows service pack (SP) revision level for this to work properly.

The /scannow option scans all protected system files immediately and replaces incorrect versions with correct Microsoft versions. This command may require access to the Windows installation source files.

How to run SFC with the scannow option

Click Start > Run and type sfc /scannow and the click OK.
Note the space between the c and the /
You may need your Windows XP CD so have it ready.
If you have Service Pack 2 (SP2) or SP3 installed, you will need the SP2 or SP3 version of the version of the CD. This can be done with a borrowed CD, if you don't have one.
Allow the scan to run and when completed, reboot the system.

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