Having the same issue with our TV right now. It just started... Pretty sure it was a bad firmware push... Unfortunately the TV doesn't stay on long enough to factory reset...
This is the 2nd time it's done this. The first time we factory reset and turned off updates since we can't trust Samsung's firmware engineering apparently. We got lucky and it stayed on long enough to get through factory reset.
No idea why it broke now. Maybe they forced an update?
It's really frustrating... Especially since we know it's a software issue. Next TV is definitely not going to be a Samsung.