Solution #1


1. At first remove the back cover and the battery for a couple of seconds.
2. Then put the battery and the cover back in.
3. Finally, power on the phone by holding the Power button.


Solution #2


1. If the display is off, press the Power to turn it back on.


2. Afterwards press and hold the Volume Down + Power button at the same time for a short while.


3. Well done! The device should vibrate and reboot.