Do you have a flat panel monitor? Is it connected through dvi or through the normal video input?
i have a 17' CRT monitor connected to the normal video output running at 1280x960
i swapped with a 15' CRT (800x600), then it started to get out of focused and the contrast and brightness got messed up
so i changed it back and the symptoms transfered to the 17 (only at the boot screen)