You need to see if it needs windows re-loading - leaves data intact on re-install - this assumes you do not have a bootable cd to hand.
That's what I had to do ~ reload XP (which process automatically erases the old version) ..... but it lost all the saved data, address books, favourites etc etc. We thought we had saved them to a "stick" during the process but when we came to put them back in all it held were the headings/file names etc. Contents all gone.