With these new fancy, modern TVs you have to tell it what you want to watch - which signal to process.
When I switch my TV on I get several choices DVB (digital TV from the roof antenna) AV1 - AV2 - HDMI 1,2,3 etc.
There's a button on my TV remote (TV/AV) sometimes it's called Source - Sometimes the control for this is on the TV itself.
Your TV is bragging about the quality of the picture it can show but you get no sound because you've not told it what you want to watch and listen to.
Good luck...
Peccavi
April 2013