I bought the GOTY edition on Steam during the Christmas sale, but never actually played it until a few days ago. I had quite a bit of trouble regarding crashes initially, but they seem to have fixed themselves.

When I started the game up again, everything was going fine. I actually made it to Arefu last night after disarming the bomb in Megaton, everything seemed fine.

When I tried to play ~20 minutes ago, GFWL popped up out of nowhere and asked me for the game's CD key. I alt-tabbed to Steam, got it from there, and put it in. Validated just fine. But now my saves are gone. No quicksaves, no autosaves, no manual saves. Nothing.

I knew Steam Support wouldn't help with a third-party issue, so I came here. I'm not sure if this is a FO3 issue or a GFWL issue, but if anyone has some way of helping me out, I'd be extremely appreciative.

Copy the saves from "My Games\Fallout3\Saves" to "My Games\Fallout3\Saves\[GFWL username]".

That did it. Thanks.