- Press and hold the volume downvolume down and PowerPower buttons at the same time until you feel a vibration (about 10–15 seconds).
- When you feel the vibration, release the buttons, and then immediately press and hold the volume downvolume down button until you see a large exclamation mark.
- Once the exclamation mark appears, press the following four buttons in this order: volume up, volume down, Power, volume downvolume up, volume down, Power, volume down.
- Your phone should now reset and restart itself.
- It might take a while for the reset to finish.
- Go to Settings->About page.
- Press resetReset the phone button.
For further reference see these webpages,