I have a problem, started a few months ago, where I'll be watching something and just can't see details in dark areas. For example, Game of Thrones, in a dark scene, I'm lucky to see faces, but clothing and such at night, just black masses.
I discovered, if I click into the menu, scroll down to I believe it's 'video' it brings up a screen and says USB not Found... because no USB plugged in. When I exit out of the screen... voila... the screem is back to how it should be. I can see folds in the cloth, details in the back etc.
I though maybe it was something to do with the ambient sensor, where it auto adjusts brightness, disabled it and no difference. Reset the video options to default, which I always had them set to anyways, but nope, next time I turn the TV on, if watching something dark, I have to open the menu, click video, wait a second, exit out and it's fine again.