After attempting to install Halo 1 and Halo 2 on a different computer for the second time, I was told that my product key was invalid. I've read that Halo 1 product key has an unlimited amount of uses and I'm not sure about Halo 2, but I should be able to at least install it twice. I can't play multiplayer with the current product key I have for Halo 2 and have even contemplated buying a whole new game for just the product key to resolve the issue, even though I haven't.