We downloaded a WinXP Pro reboot disk and the Win XP Pro start-up disks from MSFT's main website.  Put them on six floppies and then we tried to re-load Win XP Pro as one of the options given after the installation of all six disks.  It wouldn't allow us to do that because of a missing or corrupted file so we re-booted and re-loaded all six floppies and then selected the repair option.  It claimed that it could not make the necessary repair because of a missing or corrupted file.   So we referenced the help section to try and understand all the commands to see if we could use any of them and we decided to wait rather than to proceed since we did not know what the hell we were doing.  I mentioned in my initial OP that my son had manually deleted some files, but he has since stressed to me that all he did was delete some Ad-ware programs that could only be completely deleted by re-booting.  Only problem was that when we re-booted we could only get as far as the user sign-in with the password.  Cute piano notes  would indicate we were signing in along with the 'loading your personal settings' display soon to be followed after about five seconds by not-so-cute piano notes  indicating that you were logging off.