yea, I have this problem when I overclock my video card that isnt stable , or The video card is overheating , or The drivers are $hit and reinstall.
Its doing it becuase, your playing you game and than the game freezes right? well that is becuase overclocked video card and it isnt stable , or The video card is overheating. Than the drivers knoe that the video card stop working so the drivers go to the lowest setting and lowest bit colour, so the video card can work lol. than you restart