When the monitor brightens up, does the video appear like a wishy washy? This happened when I had my very first Pentium 166 in 1996 and the monitor I used was a Mag Innovision. The card I had was a 4MB Matrox. From what I remember the true bit was set too high and that's what caused the screen to appear wishy washy. I had to download the new video drivers and then I had to adjust the color quality by lowering it to the next level. That fixed the issue. I am not sure if this is what is happening to you, but it might be worth to try it. What monitor do you have and what is the video card?