I would say do a repair install of windows.
that will most likely fix your problem.
How to do a Windows Repair
1. Go into your computers BIOS and set your boot order to cd rom first (usually DEL key, or F1, F2,)
2. Put the XP CD in the drive and save and exit the BIOS
3. Press a key when you see the screen that says press any key to boot from CD (right after the POST)
4. let windows load its files
5. press enter,(not R you dont want the recovery console)
6. then press f8
7. then press R for repair
8. and let the repair process begin.
good luck man