Insert the Windows® XP CD in your drive. (Hold down the Shift Key to prevent it from starting.)
Go Start > Run ...in the box type in sfc /scannow …please take note of the space between the sfc and the /.
This is the System File Checker...it will scan all the Windows® core system files to ensure that they are in their respective correct places, and if not replace them from the CD.
During the scan you may be asked to Insert the CD, if this happens just go retry and let it do its thing.
One important point: While sfc is running, it is not advisable to do any other work, or have any browsers/programs running on the computer, until the scan is complete. (This process will generally take around 45-65 minutes to complete).
Once finished, remove the CD and reboot your machine...all should be "Normal" (hopefully).