I suspect you've already tried unplugging power sources for a few hours to reset, but I will share a crazy story.
One night about six years ago, everyone in the house was awakened by a crazy persistent noise. Turned out, it was coming from our tv (we usually only have one) . Unplugged it. Moved it the next day to a tabletop in another room. Bought a new tv.
Our daughter wanted to watch something different one night, a couple months later. Plugged in the crazy old tv, and the cable connection, and, voila, after channel scan, old tv worked like a charm.
Just for grins, before i spent more money, I'd disconnect 110 and 12 v power, and let it sit awhile. If a main board is fried, it won't help. But if you're not going anywhere for awhile, doesn't hurt to try to reset it.
Power fluctuations can do weird things to tvs.