A lot of the time when I exit an application with a full screen (i.e. game) My windows locks up and I can't press anything on the toolbar, or any of the icons on my desktop. Also I sometimes get a black screen and the same thing happens. Ctrl + Alt + Del doesn't work. However if I press the power down button on the PC it shows up the ctrl + alt + del screen and shuts down properly. I suspect its the video card which is a 6800GS. I have the latest drivers from November.