My Note 4 has suddenly started turning itself off when I unplug the charger. It is fine when the charger is plugged in but as soon as I unplug it it powers off then when it tries to power back on, gets as far as the screen with 'Samsung Galaxy Note 4 ... powered by Android' on, then tries to reboot again and simply continues doing this every few seconds. Yet when plugged into the charger it is ok. I have tried factory reset etc but no joy.