[Activating a game in GFWL Client]

hmm normaly if you have a game on steam and that game is using GFWL then you should have the key that pops up everytime you lauch the game, have to create an account on the GFWL client, then enter the key

You can do it in game by selecting "Redeem Code".

Or you can do it online here: https://live.xbox.com/RedeemToken (Make sure you are logged into the right account!)

Like has been said, this has to be an actual marketplace code and not a Live key.

if you bought the game from steam, once you open it and sign in, it'll ask you to enter the CD-Key