ni4ni,
i don't know a fix for what's happening but one way to fix it for sure is to do a re-install. I know, its not the ideal thing but its the only thing that will work for sure. If you don't want to redo all your programs then do a repair. It will install XP and keep your programs (in case you don't know). Make sure you say no to the first repair option on install (thats the recovery console, you don't want that!) it will detect an OS on your C:\Windows\blah blah, it will ask to hit enter to repair.
That should fix your problem. I have experienced this many times and the only solution is a reinstall. sorry,