Ok so I read through a lot of this stuff and tried the 'helpful' answers, (thanks guys but it didn't work with my samsung s5.) My problem was the same as most, a flickering screen and a horizontal green line when on 'auto', meaning I had to manually adjust the brightness.
After a lot of restarts I gave up, had a vino, then deleted my free alarm clock app, then did a restart again. It worked! Now I'm not a technical wizard by any stretch of the imagination but maybe it is an app that is running in the background of your device? Hope this helps somebody