I had the same issue and tried the suggested fix by Will. Didn't work or took time to work while I tried the following on my new Samsung TV. I pressed the 123 button on the Samsung remote and changed from 6 to 1 then 2 then 3 then 4. Each time I tried the connect to cable box/ HDMI1. TV was stuck on a series of horizontal dots, restarted TV. I hit the house symbol button and saw "Cable box" as an option. Then both the remote that came with the cable box and the remotes we normally use from our cable company (Spectrum) would change the Chanel and could see the guide when pressed but no sound. Restarted TV again and selected Cable box again and sound started working. I did all of this and had this issue after connecting to wifi and downloading the hour long update before seeing all the free available channels. Either it was a super slow plug and play update from Will that eventually worked while I was monkeying around or something I did helped so thought I would add it to this post even though not sure the exact process or what I did to get the cable box to show up.