Halo 2 Product key

Hallo ich habe ein Problem
Ich habe mir vor Jahren Halo 2 für Windows Vista gekauft und den Produktschlüssel auf einem anderen Computer benutzt und nun kann ich diesen nicht mehr nehmen. Kann mir jemand helfen?

I bought a few years ago Halo 2 for Windows Vista and used the product key at an older Computer and now i can not use the same a . Can anyone help me?

Have you installed the game more than 3 times? As far as i know, a key can be used 3 times before it becomes invalid.
However, if you have other Games for Windows Live games (like Resident Evil 5, GTA IV) try using their keys, as they can actually work for Halo 2.