Try disabling the Steam Community Overlay thing in the Steam client.I have the same problem where the game won't launch through Steam but I am on Mac OSX 10.9 and this problem didn't exist a few days ago. I can launch the game but can't use steam overlay or get access to my cloud save games.
I have done a complete re-install and am completely stumped at how my game was working fine a few days ago and now isn't. I haven't changed anything since I last successfully launched through steam.
Try disabling the Steam Community Overlay thing in the Steam client.