Nokia Lumia 520 hard reset Windows Phone 7
1. Turn off your Lumia 520 phone.
2. Press and hold the Volume down and Camera keys.
3. Press and hold the Power key.
4. When you feel the phone vibrates, release the power key, but keep pressing the volume down and camera keys, until the phone reboots. All data will be lost!
nokia lumia 520 hard reset
Nokia Lumia 520 hard reset Windows Phone 8
1. Turn the power Off.
2. Press and hold the Volume down and connect the charger or the USB cable with PC, for about 8 seconds, you will see an exclamation mark (!) on the screen. Note: If you do not press any of the following keys, then the phone wp8 will starts boot normally.
Then press the keys in this exact order:
1. Volume up
2. Volume down
3. Power
4. Volume down