Instruction I:
1. Begin with some manual work. Carefully remove the device's back cover and battery.
2. Do nothing for five seconds and then put everything back in place. Press the Power button.
Instruction II:
1. First, press'n'hold the Power button until a menu will appear.
2. Second, select the Power off option.
3. Wait for a few seconds and then press'n'hold the Power button until the phone turns back on. Done!