I have a Vizio VL470M. Recently, it stopped working with HDMI
cables, first the audio went out and then the picture as well. I tried three different cables in all four ports with both a cable box and a PS3, so I'm certain it was the tv and not the cables, ports, or devices. The tv continued to work with the cable box through a coax cable for a few days until the screen began flickering to black, and then quit altogether but the sound continued to work fine.
I shined a flashlight on the screen and do not believe that this is a backlight issue. I also tried all the normal tricks of unplugging all the cables, holding the power button, etc.
After some research I assumed the inverter board needed to be replaced, so I ordered a new power supply board through ebay (apparently the inverter is built into this board). I just replaced the power board and the tv appeared to be fixed - it flickered a few times and then worked perfectly through the coax for a few minutes until I tried the HDMI cables again. It gave the same HDCP error message as before, then began flickering to black progressively worse until nothing just like before. It is still occasionally flickering on, but is black almost all the time.
I'm out of ideas except that my HDMI cables killed the brand new board immediately, which would be unlikely since they worked with the tv for years previously.