After installing Halo 2 Vista, I was asked for the activation key, which I entered and it said my Halo 2 was activated successfully. Then I started the game and was confronted with Games For Windows Live sign-in and it said "Can't sign in because your product key is not valid. Please enter a valid product key." I have Xbox Live and I bought the game legally. The product key worked on my old computer, which I have played Halo 2 multiplayer on before.