Reset your Lumia phone with Windows Phone 7.
Warning: Resetting your phone erases all personal content, including apps, and restores the factory settings.
- Make sure the charger is disconnected, and switch the phone off.
- Press and hold the volume down and camera keys.
- Press and hold the power key.
- When the phone vibrates, release the power key, but continue holding the volume down and camera keys, until the phone reboots.