what video mode you running? if its software i suggest you change it to openGL or direct3d, if its direct3d i suggest you search the fourms for the solution, this flaw has been answered many times, if switcing to these vid modes dosn't help, its probably becuase you either have a very bad video card or proccesor and its overloading them, or you have no video card at all.
Edit: one more possiblitiy, your video card fan could be so dusty that its over heating and crashing the game