[ChrisH09]

Which one did you uncheck? There is two settings in there for when your phone is plugged into the wall/computer and when your phone is only on battery....make sure the one you unchecked is the one that was on battery power. Also this phone has a proximity sensor that will dim the display and or make it go off if it is close to your face or object. It's also sensitive to light...so at night time it will get brighter, while during the day it will dim a little more.