I think I have the same problem with my 50 in LG plasma. My electronics skill is basic, took the tv to service anyway, and they said “probable lighting surge through the hdmi connect” They said best case scenario is to try to put replace the motherboard or send it off to be repaired MAYBE but it would cost $250. Not worth it in my opinion. I hate to add to electronic waste but unless its a straight forward board swap from eBay, it may be a done deal…
Any advice is appreciated.