I had the same issue, Then i started spamming Alt + f4 or alt tabbing and closing it via killing the process in task manager.
Needless to say many people are experiencing the issue and its caused by the memory leaks of the game. At least thats what 'we' (the people experienceing it) narrowed it down to.
When i alt+tab , something pops up saying i need to change resolutions. Im running windows 8 64 bit by th way. if that helps.