New DTA but now remote won’t change channels

One of our TVs using a DTA lost sound while watching it. It's a Sharp smart tv and the sound works fine when watching Netflix over wifi. After troubleshooting with Advanced Tech Support still no sound so a tech came out today & replaced DTA & still no sound. He ended up hooking up the new DTA to a small tv he had with him and was able to get sound so tech says it's a problem with the tv. Sounds plausible although I don't understand why tv has sound when using Netflix on wifi. Anyway, after tech left I went to do some more troubleshooting and discovered that the remote won't change channels.  Remote powers tv on/off & moves volume bar on tv screen (though no sound) so seems like remote is paired with the tv but, I paired the remote again and still can't get it to change channels. Not sure what to do next. Also, if anyone has any ideas as to why TV lost sound altogether using DTA only I'd appreciate any input. Note: the DTA is connected to the tv with a new HDMI cable. Thanks!