if is not water damage , apple should repair it. If not well open the iphone go to youtube see vid how to open it. turn off iphone open it just pull off #1 and put back in. that's the lcd connector. This should work if not take #1 then #2 and # 3 put all conector back that should work. #1 Lcd conectot #2 is the Digitizer
#IS the ligth. If you got gray lines the lcd may be broken.