Check out the cable.
First off I know very little about setting up TV's, but learning.
I had the exact problem you are having two days after I hooked up my new Samsung TV, NO SOUND one morning.
I was using HDMI cables from the Dish Network box to the TV. The cables are fairly heavy and I found that one was hanging free from about 4 feet vertical from the box to the TV, It was slightly skewed (not totally in) and would not change till I took some of the weight off the cable by putting a plastic tie around the power cord and the HDMI cable to stop all the weight of the cable from just hanging from the connector. This immediately fixed the problem. I hope this helps you.