From my experience it is often moisture that causes these types of problems... After my girlfriend had this problem with her Note 4 this afternoon, I did some googling and ended up here. My fix was to turn the oven on... Getting the temp to about 60 degrees Celsius... Take the back off the Note 4 and battery out Remove the sim and external SD card Place the phone in the oven for 30mins After 30 mins remove and allow to cool Put it all back together and presto Working fine now!!!!! The Girlfriend is HAPPY!!! :) Regards, The Boyfriend.