Use System Restore
System Restore in Windows XP might not have been the greatest tool, but since Windows Vista came around, it's been an excellent choice for fixing up all sorts of problems, including issues that cause your system to not boot anymore. While testing, I once deleted a bunch of files in system 32 to purposely cause a blue screen of death, and then used System Restore to get the system up and running again in minutes. If you're unfamiliar with the process, you can follow this step-by-step guide to restoring your PC with System Restore.
