If you don't see the first three screens from the guide I link you to, cancel out and let me know.
Try this REPAIR to your installation of XP. This procedure will not damage or change your current files or settings...it will just repair or replace damaged system files. You will be asked for your Installation CD and may be asked for your product key. Follow the instructions carefully...print them out if you can. Note: This option is not always available on OEM Recovery Cd's