Test to make sure it is the monitor and not the video card on the computer.
Swap out the monitor or try it on a different computer to determine which one is the problem. If its the monitor, most monitors have a reset or auto-calibrate. Refer to your manual for instructions. If that fails, replace the monitor, do not attempt repair. Monitors contain several electronics that are much more dangerous and deadly that you find in most electronics. Don't fool yourself by thinking "I've opened my computer and changed pieces!". The big difference: Monitors can kill you even when powered off and unplugged, computers typically cannot.
