Welcome to Android Central! Pressing and holding Power and Vol Down will force a shutdown when the phone is frozen in a powered on state. But if you press and hold Power and Vol Down when the phone is off, it will bring up Download Mode (although I think for most Samsung phones, it's Power, Home, and Vol Down). If you find yourself in Download Mode, you can ignore the "Do not turn off!" message if you're not connected to a computer via USB, and just force a shutdown again by pressing and holding Power and Vol Down for 10-15 seconds. It is unlikely that you damaged your phone.
Can you give more details about how the phone wasn't charging at first? Had the battery been totally drained? If so, you may have to charge on a wall outlet for at least an hour or two before the phone will even turn on.
03-17-2017 01:55 AM