To eliminate the possibility that the monitor itself is bad (cold solder
joint, etc.), try using a different monitor for a while. If the problem
persists with the new monitor, it's possible your video card is failing when
it heats up. Have you checked to see if the GPU fan is operating correctly?
Are you monitoring your system temperatures? You could be experiencing
heat-related failure. Is there any event pattern, such as the problem
occurring when you are doing something that stresses the video subsystem,
such as playing games?
