cd key

ive resently got halo combat evolved and campain works fine but when i try to use multiplayer it says “your cd key is invalid” how do i fix this?

> ive resently got halo combat evolved and campain works fine but when i try to use multiplayer it says “your cd key is invalid” how do i fix this?

how did you obtain said key? if you didnt buy it, your outta luck. and if you did, u would need to check to see if you have it on any other computer. past that idk