XP Maximized: Use The System File Checker To Repair Files
If you're regularly encountering errors (such as warnings of missing DLL files or programs not loading) and you think that some part of Windows XP may be to blame, you can check your system files to make sure they're in good order.
Go to Start>Run and type in sfc/scannow. This will check all your crucial Windows system files to see if they've been edited or modified. If they have, it should be able to replace them with backups, but if it can't find them on your hard drive then it will need to copy them from your Windows XP CD.
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