Check cables first. If a cable is to blame you jiggle it and the picture comes and goes or certain colors come and go. If the picture disappears and the power LED on the display is blinking then it does not detect the video signal or the signal is outside the operating synch range. If you have a spare display kicking around, swap displays and see if the problem returns with the other display or if the display on a different computer does the same thing or behaves. Lastly dirty power can affect this, such as a client of mine had where every time his mom ran the microwave in the kitchen his computer would act up. Problem was that the bedroom was an expansion to the home and they decided to tap into kitchen power instead of sending a new feed from the breaker with its own service to that room. So his display ( CRT ) would make a click noise and black out and come back on each time the microwave was turned on because of a low voltage spike from the 1000 watt draw plus whatever else was on that line in his bedroom etc. His solution was getting a UPS to filter and condition the power. Do you have a UPS ( aka battery backup )?
