How to Factory restore Nokia Lumia 635 920 520 530 630 625 620 720 820 600 710 800 900
Restore to factory settings:Reset your phone. This restores the factory settings and erases all your personal content including apps you've purchased and downloaded (you can re-download them afterwards). Back up all your personal content before restoring to factory settings. There are two ways to do Factory Reset.
A. If you can switch your phone on:1. On the start screen, Go to Settings > about > reset your phone.
B. If you cannot switch your phone on
( Mobile Restarting Continuously / Blue Screen / Or Not Booting )1. Disconnect your phone from the charger.
2. Press and hold the volume down key and connect the charger. An exclamation mark (!) is shown on the screen.
3. Press the following keys in order: volume up -> volume down -> power -> volume down.
Your phone resets and boots up automatically. This may take several minutes.