Using the System File Checker

Please make sure before you try with this commands, Windows XP CD with you
You can run the System File Checker to verify protected system files.
Command line switches are:
sfc [/scannow] [/scanonce] [/scanboot] [/revert] [/purgecache] [/cachesize=x]
/scannow - Scans all protected system files immediately.
/scanonce - Scans all protected system files once.
/scanboot - Scans all protected system files every time the computer is restarted.
/revert - Returns the scan to its default operation.
/purgecache - Purges the Windows File Protection file cache and scans all protected system files immediately.
/cachesize=x - Sets the size, in MB, of the Windows File Protection file cache.