Hi so i got a free pc from my friend and he had windows xp on it. He removed the harddrive because he wanted it but i put a new one in with xp. I know its going to ask me for the activation code which i was hoping i could use the one on the case. He said he reinstalled xp once already, but can i still use that key as many times as i want? As long as the mobo, hdd, or software dosent change? Thanks