It might be something like the problem i once had...your running at 1600x1050? I once tried cranking my X850 XT to super high rez in CS: Source and i started gettting this little purple lights. They would sit in one place of the level. They werent big, maybe an inch or so across. They didnt move with the screen, it was as if they were built into the walls/floors/ceilings. Turning the rez back down solved the problem