Excerpt: "When I upgraded to Windows 8, I had issues upon starting known Games for Windows LIVE games, the overlay would not start. Therefore, effectively locking me out of my games by not being able to access my (online) profile. The game saves were still on my system that I copied over, but due to some incompatibilities with GFWL and Windows 8, would not allow me to play them.
This is a way I was able to fix GFWL on Windows 8 (Pro). It may or may not work for you, so don’t take this as the definitive fix"