Whoever had slammed your phone has caused the problem. '''Get a new screen.'''
+
+
=== Update (02/02/2017) ===
+
+
Is it cracked? How long have you been using it? If you have been using it for a long time, try getting a new battery. If it's cracked then you should get a new screen. If it's not cracked then open it and if there isnt a wire connecting to the screen, look at a teardown to see what goes where.