This is a graphics issue generally caused by an unsupported video card. Make sure your computer has a NVIDIA 8800 GT video card, an ATI Radeon HD 3450 video card or better. You can also try to download the latest driver available for your video card from the video card manufacturer’s website.
If your computer meets the requirements, after changing the resolution (if necessary), reboot the game so that it can properly consider the change and avoid using the “Alt+Tab” key combination.