I've seen several "fixes" online. Maybe they are just outdated. But they are all temporary fixes, and sometimes, depending on your TV model, might now work at all.
Here's what to do if the "change brightness to Normal" doesn't work . . .
You must do this in the order below. If you mess up, just hit HOME one time, so you are on the HOME page. And then start over.
At your HOME screen: press HOME 5 times. You should hear a blip each time.
Then press UP ONE time.
Press REWIND (on the left) 2 times, then FAST FORWARD (on the right) 2 times
You should see the screen resetting for a little bit, then stop.
Wait a few seconds, and hit HOME again.