The game engine has a problem with the latest nvidia driver v.347.25. Graphics become completely broken. This happens at the worst possible moment - in the time of Steam release. That is the price I pay for using my own custom engine. The solution for now is to downgrade to older driver version . v344.11 is safe. I am working on it and will let you know when the bug is fixed.
You can get the driver from here
http://www.nvidia.com/download/driverResults.aspx/77837/en-us
Jan