css screen goes black

[Before]

Whenever I open Counter-Strike: Source it shows the background image of the two CT's until it loads then the screen turns black and when I scroll over the buttons (ex. find servers, options, exit) i hear the sound of scrolling over them.. but the screen is black and i cant see anything when i alt f4 out i get the error

the instruction at "#" refercened memory at "#" the memory could not be read.


any help would be greatly appreciated..

thanks