If you can get web access easily download a win 98 boot disc from bootdisc.com (might be spelled with a K) anyway put it in and restart pc when it starts up it will ask if you want to restart the computer with cd select yes
It will then go into another screen with A:\ when this appears type in format c:
This will wipe the entire drive ready for win xp to be installed.
If format c: wont work try it without the space.
it will say all data will be erased from disc just hit Y then enter and then it will say something bout enter amount of characters leave blank for none just hit enter at this too.
Once its wiped just follow the instructions for reinstalling again. If you need anymore help give a shout and il help if i can.
Paul McGill.
July 2005