Your computer should have some sort of rescue disc (or discs) that came with it (if it was new). Some computers also have a restore partion (like mine) and prompts you to restore when you first boot the computer (before XP comes up your screeen would read ‘press F(something) to restore partion’ or something to that effect. If this is not a new computer or you have lost your disc(s), use your Win XP disc to reload Win XP with XP defaults.