Apple TV worked until today. Message says unsupported signal check your output device. I have checked hdmi cable with another device and it's fine. Put on a different tv and same message. Went out yesterday and bought a new Apple TV and same problem.

Just got apple support on phone. Solution was to turn hdmi cable around and it worked!

Tried that.... Nothing. Unplugged everything and started over again. Nothing. Veryyyyyyyy frustrated. We have a Sony Bravia..... Tried on our Panasonic and same problem. Have used on the Sony TV for past year and worked fine.

I am going to replace the cable. It works perfectly with our ps3. I had unplugged it several times and plugged back in but the solution was to turn it around. Since I've done that it is working with the Apple TV. Another source has said sometimes monster hdmi cables have a preferred end. Makes no sense but it worked