Video card to sound receiver to HDTV suddenly stopped working

I currently have a GTX 570 that connects to a Sony HT-CT 150 home theater system, which in turn connects to my LG HDTV, all via HDMI. I also have my GTX 570 connected to my PC monitor. This set-up has worked great for over a year, allowing me to use my TV as a second monitor or duplicate the display from my PC and play games in full HD and 7.1 audio. However, over the past few days my TV has been flickering on and off at random intervals while being used as a monitor. Now, the TV will go to "No Signal" after a few flickers...usually about 10 to 15 minutes after enabling my TV to duplicate from my video card.

If I go back into the Screen Resolution menu in Windows and set the display output to just the monitor, and then back to duplicate, about 50% of the time it'll duplicate again with the flashes before eventually going back to no signal.

Any help is REALLY appreciated.