Hard Reset your Windows Phone

If your phone is unresponsive and you can’t reach Settings Settings icon, you may be able to reset your phone using the hardware buttons. On Nokia Lumia phones (and some others), do the following to reset your phone:

  1. Press and hold the Volume down Volume down button and PowerPower button buttons at the same time until you feel a vibration (about 10-15 seconds).

  2. When you feel the vibration, immediately press and hold the Volume down Volume down button button until you see a large exclamation mark.

  3. Once the exclamation mark appears, press the following four buttons in this order:Volume up Volume up button, Volume down Volume down button, Power Power button, Volume down Volume down button. Your phone should now reset and restart itself. (It might take a while for the reset to finish.)

http://www.windowsphone.com/en-au/how-to/wp8/settings-and-personalization/reset-my-phone