XP Key is invalid

I recently bought a computer from a company that was going out of business. They wiped the hard drive so there was no information left on it. They said that the xp key on the label on the side of the case was valid and all I had to do was reinstall with a xp cd. I have a few of them sitting around so I tried to install with the key on the side of the computer and it says that the key is invalid. It isn’t trying to activate and saying that it is bad, it is simply saying that the key is invalid when I am trying to insall windows. I can’t even finish the installation. Have any of you ran into this problem or have any ideas as to why this is happening and how I can remedy the situtation?