In that case, you may need to factory reset the phone, which will erase everything on it. Before you continue, be sure that you have the correct SIM card in the phone.
Factory reset using the hardware buttons
1. Turn off your Galaxy Note 4.
2. Press and hold Power, Volume Up and the Home button until you see Recovery booting in blue at the top of your screen. Release the buttons when you see the recovery screen.
3. You'll now be in Recovery Mode. Use the volume buttons to scroll up and down and the Power button to confirm. It's not a bad idea to wipe the cache partition while you're here, but it is not essential.
4. Scroll down to Wipe data/Factory reset and press Power to confirm.
5. Scroll down to Yes and press Power to confirm.
6. You'll see a notification in yellow at the bottom of the screen to confirm the reset has been completed. Scroll to Reboot system now and hit Power to confirm.
7. Your Galaxy Note 4 will now reboot.