I recently built a computer from scratch. I bought all of the parts on NewEgg.com put it together and installed Windows XP using the disk from my old computer (one I am replacing) To install Windows I used the key from the old computer. I will not be using that computer anymore, hardrive will be wiped and given to a friend. When I attempt to activate windows it says the key is invalid. I don't want to buy Windows XP again when I have a legal version from my old computer. Is there anyway I can use the old key? The computer is a Compaq if that has anything to do with the problem.