Just so you know, I did a full uninstall and reinstall and it's working fine since then, but I did that before Neil suggested another way which is probably quicker.
Same. Tried other games, they work fine. But I'm having this issue too. Whenever I try to start it the steam bootstrapper stops working, and then after that it tells me the game is running when it's not. I've deleted appcache, done several restarts, done all that. It's just FM.