I bought a copy of Doom 3 on Steam today (with it being on sale and all, and It being in the spirit of QuakeCon.) and for It won't take the key-code I enter. The game already has the code entered in, and I've tried entering it manually, but it still says it's invalid.
Any ideas?
Contact Steam support: https://support.steampowered.com/
Tickets can take a while to answer, which is annoying, but they are typically very good at helping you out. They once refunded me a game which technically is against their policy. Hopefully they can just send you another key, and who know, you may even get something addional for the inconvenience.
I had this problem before. Try verifying the cache.
I did what you guys said, and no luck. My friend told me to try and go to where Steam is installed and manually entering in the key. So >\steamapps\common\doom 3\base folder, Then open the 'doomkey' file and set it to Read Only which seemed to work, but thank you guys for offering help, I appreciate it :)