Try a different monitor.
Try a different cable.
Since the gpu now has to work harder to drive two monitors make sure the innards are clean.
If this is a desktop test with the side panel off.
Hi all,
I work from home and decided to use a smaller tv that we had as a second monitor. When I initially plugged it in, everything worked fine for about 4 hours, then my screen started tearing and changing colors (it seemed to just melt from the top down). I have been trying to figure out what to do and have read a few post about the resolution and refresh rate, but can't seem to find a setting that fixes it. Help!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic