Serial Key

[BadassWalrus]

So the game just asked me what my serial key was when i tried to join a multiplayer game. I have had the game for years so i dont know why it all of a sudden asked me.

I read a thing online that i can use one of my friends (couldnt find my actual serial key) So i entered his in and now we cant play on the same server.
Is there any way i can get my first serial key back?

PS: I bought it from amazon, not from steam

also i still have my activation code and a hardware hash code. (i dont know what the hardware hash is)

 

[Norwegian]

I am not 100% sure whether or not this would work, but you could possibly try re-installing your game.