Sometimes the simplist solution is overlooked. This won't work all the time, but I kick myself everytime it works because I tend to use it as a last resort. Just completely unplug the monitor. Give it 5 to 10 minutes time to cool down. Replug and try again.
I have been amazed at how often this will work for any number of "glitches" in electronic items. I have even been told to do this numerous times by tech support people. It sometimes has to do with boards or curcuits "resetting" themselves after being unpowered, sometimes it is "softwiring" that resets, and sometimes has to do with a "heating" problem somewhere in the circuitry. If it is a heating problem, then it most likely will return.
Hell, it's always worth a shot as a last resort.