Hello Rich,
sounds like you have either a corrupt file or possibly corrupt ram.
there is a possible fix, if its a corrupted file, you will need your winxp install cd & it must be bootable. make sure your not using the restore cd that you get with some pc's that have pre-installed windows on them.
goto
http://www.michaelstevenstech.com/repair.txt
navigate down tot he bit that says XP REPAIR INSTALL
and follow it through im sure this will solve ur issue.
hope this helps.
-=Saj=-, February 2008