Hello there,
This is actually quite simple to fix if you have system restore activated. What has likely happened is that a key in your registry is corrupt. Anyways, here are the steps to fix it.
1. Reboot your computer, and tap the F8 Key while booting to bring up the boot up menu.
2. From the menu, select "Safe mode with command prompt".
3. Now type \Windows\system32\restore\rstrui.exe into the command prompt.
This will allow you to revert back to sometime when your computer was working fine before.
Once you revert back and get things back to your current settings (best of your ability), I would consider manually creating another system restore (although xp regularily does it automatically, I would feel much safer doing it myself after taking the time to update my settings back to how I want them).
You can go about this by going into the start menu, then programs, then accessories, then system tools, and then into system restore. From there you can create it yourself.
I hope this helps you out. If you didn't have system restore activated you could always try to repair windows using the windows disk, or ultimately reformatting which would take approximately 95 minutes and then additional time to update xp from windows.com. The only down side is losing all of your stuff. I always like to keep backups, and am very glad to have a second hdd installed.
Regards,
-Emily