Some time our mistakes or Proper Shut Down or some Virus makes Windows XP corrupt system files. You can easily fix them. You only need Windows XP CD.
1st, Place the xp cd in your cd/dvd drive
2nd, Go to start >run
3rd, type in sfc /scannow
You are done now. It will scan for corrupted system files and fix them automatically.
NOTE: It is only tested on Windows XP. You can also try in other versions of Windows.