Hello man! First of all you should go to the system setup which you get by pressing F10 after restarting the computer. And make sure that your BIOS and RAID setting is OK. I mean if it is set to the windows 7 then only windows 7 can run and windows xp cannot be installed and if it is set to windows XP then only windows XP can be installed. I think by following these instruction you can easily installed windows xp on your PC.