Nokia Lumia 800 hard reset

Turn off your Nokia Lumia 800. Press and hold the following buttons Camera + Volume down + Power until your phone vibrates, then release only the Power key and keep pressing the Camera + Volume down for a couple of seconds 4-5s.
or

1. On the Start screen, tap .
2. Tap Settings > about phone.
3. Tap reset your phone, and then tap yes.Repair Nokia Lumia 800 do one of the following
   • Reboot your Nokia 800 phone. Press and hold the power key for about 10 seconds. The
   phone switches off. To switch your phone on again, press the power key.
   • Update your phone software
   • Restore the original factory settings