Apple TV functions as Airplay target, not independently
As mentioned by cloneman it sounds like there is a Communication Problem between Apple-TV and the Reciver or the Reciver and the TV.

Maybe its like on my Setup (i have an older TV which doesn't Support a Resolution as high as the AV-Reciver)

So if i turn on The TV first than the Reciver than Apple-TV it works as it should. (cause the Reciver starts after TV it knows what Resolution the TV supports - he can ask if not)

If i turn on the Reciver first than the TV it doesn't show but audio works (cause the Reciver directly plays the Audio also it gets the Video and passes it out but in a to high Resolution so the TV can't show it)

Maybe you can try out different sequences of turning on (and find a way that works for you)

If not try this (most of todays TV's have more than one Input and also most of the AV-Recivers have at least one SPDIF Input) assuming yours also. Connect Apple-TV via SPDIF to the AV-Reciver and via HDMI to one of the HDMI Inputs of the TV direct.

So you give the Apple-TV and the TV the possibility to directly communicate and they should be able to handle out a resolution that works for both.