My laptop come with windows xp media center2005 and I have virus that forced me repair the windows. My friend offered to use his windows xp PROFFESIONAL to repair window and everything was fine until the the part i have to enter the Product Key. I used the old product key on the back of the laptop and his product key that come with xp professional and none or them work. We could not find a working product key for this and i think the problem is because i upgrade the OS from media center 2005 to professional. Can someone help me with a working PK or show me how to reverse back so i can log into my computer?