Do a Windows repair install
If you have serious problems with XP performance, or you get errors, some system files can be damaged.
A repair installation re-writes all essential Windows XP system files and re-detects all hardware without affecting the registry, current desktop settings or user data stored on the hard drive. This is the only way short of a full installation that can recover from errors caused by installing a different motherboard in an XP system, for example.
To perform a repair installation:
Boot the system from your XP CD.
Choose the 'press enter to set up Windows XP now' option.
Press F8 to skip through the EULA (though if you haven't read it before, you should now. See our legal article for details as to why.
Now press R to begin a repair installation.
Your system will go through the entire XP install process, but will not attempt to replace any of your existing data. It will simply reinstall the vital system files, fixing any that are corrupted or missing.
Please post back if you have any more problems or questions.