The reason I ask, is that I sometimes get this when I reduce the color depth of the screen to 24bit color...
Rather annoying, so I keep it on 32bit.
Try increasing the color depth.
If you can't get it on 32bit, (ie. max is 16bit or 24bit), reduce the resolution of the monitor and try again.
Monitors have own amount of fixed RAM. Increasing resolution may cause decrease in color depth. Reversing this may help.
(Resolution is 1024x768, 800x600, 640x480, that sort of thing)
Hope this helps...