ha ez még mindig ugyanaz a kulcsos gebasz, ami nekem is volt szeptemberben, akkor itt a megoldás, nekem így simán ment:
1. Open a browser and go to xbox.com log in to your GFWL account, click My Account then click Redeem Code and put in the cd-key you got from steam, this will tie the key and game to your GFWL account.
2. You should have Games for Windows Marketplace installed already, run it.
Start->All Programs->Microsoft Games for Windows Marketplace->Games for Windows Marketplace
Click the Downloads tab and you should see GTA IV PC, Click it and some details should appear, then finally Click "View Game Keys"
3. The key shown here is completely new, i believe it is created when you tie your steam cd-key with your GFWL account.
Take this new cd-key and use it when GFWL asks for the product key next time you load the game and everything should be Golden!