Thanks for your response.
I've tried what you saiid, to set the Apple TV to 720p with my monitor but when i connect the TV "no signal" appears again.
that I don't anderstand is the fact that it worked fine until I have this problem of HDMI cable that I replaced.
and the 2 TV hdmi inputs works well also because I can connect my "Cable Box" and my game box on both inputs it's ok.
I've tried to find something in the parameters menu of my TV (SAMSUNG) but I didn't find anything to set or test the hdmi inputs;
the only problem I had is the HDMI connector cable TV side was torn off when I tried to remove it and the AppleTVwas connected, I first thought of a hdmi output shortcircuit but AppleTV works fine on my computer screen, so it's not a hdmi output problem!
I don't know what to do .......
Did you resolve this, as I am experiencing the same, i.e. it will not show up as an input on our LG TV, but when I swithch the HDMI cable from one of my other HDMI devices such as Cable it works. Tried plugging other devices into the other TV HDMI inputs and they work.
So run out of ideas.
Look forward to a reply.