try to replace front camera flex cable..
might proximity sensor make short inside.. or flex cable anywhere..
if screen is working when u believe 100% screen was work.
mine was bad lcd screen ( might be my miss handling) and camera flex
i replaced it ,then its works well...
# symtom?
was logo coms on twice and LCD gone just dark , black but back light still on,
replced brand new then its work ,that time ,i disconnected all other cable..like camera, home button,
just only digitizer and LCD cable only.. e\works good..
now i attated camera part, same happen again.. and replaced camera part flex..
now works ok.... itune still reconize without lcd or any cable when i hook up usb on computer..
thks hope help this