Procedure to Soft Reset the Nokia Lumia Windows Phone 920 800 520 720 1020 710 625
Soft Reset:
If your battery is not removable, switch the power on and disconnect the charger.
Then press and hold the power key + volume down key for about 15 seconds until the phone vibrates and restarts.
Hard Reset:
Then press and hold the power key + volume down key + Camera Key for about 15 seconds until the phone vibrates and restarts.
