Seen as im bored i might asswell
First backup all data.
First insert the win xp disk. Reboot your computer hit delete on startup go down to Advanced Bios Features click it go down to primary boot disk using the page up and page down keys change it to cd as primary boot device, reboot and u will enter win xp setup. Reformat usin the simple wizard, when installing a fresh install of xp unplug all your USB devices etc just leave in mouse keyboard and monitor.
MAKE SURE YOU BACKUP YOUR DRIVERS.