It sounds like a Video card problem.
Are you running built-in video or a video card?
If you are running a video card I would suggest checking to see if the fan is running on it and If the cards heatsink needs a cleaning.
If running Built-in video I would look to see if the Motherboard has any fans that have stopped running or heatsinks that need cleaning.
If neither of those is the problem and you have swapped the monitor just to be sure it is eliminated then you may need to try a different video card as a test.
Edited by rotor123, 15 March 2012 - 10:07 AM.