Apple TV will not work on my Panasonic 50AX802B 4K LED

Recently i purchased a new Panasonic 4K LED TV and ATV 3rd Gen will not work.

it works on my other tvs in the house and my previous main TV.

Ive had Richer Sounds out to swap the TV, however we tried the engineers ATV 3rd Gen first....and his worked!!

tried all the usual...different HDMI ports and leads.

please can someone help me. Apple just keep telling me to reset ATV - which doesn't work.