I recently bought a new hard drive. I installed windows 7 on the new drive everything was fine until I went to register windows. I previously bought an upgrade key with a student discount. I still have my old windows xp key but when I went to register it said the key couldn't be used with a clean install. Is there anyway I can input both keys to prove that I own a copy of xp or do I need to install two operating systems every time I need to reformat?