Restore your Lumia 820 to factory settings
You can restore your Nokia Lumia 820 to factory settings by following the instructions below. This can be useful if your phone continually freezes, fails to respond or you’ve forgotten the security locks you’ve set up to access the phone.
Important: Restoring your Lumia 820 to factory settings will wipe all phone data so if you’re not locked out of the phone you should first back up your data to your PC or to your Mac, and synchronise your phone with your Windows Live account. The reset won’t delete data saved to your SIM.
Ensure that the handset is turned off by holding down the power button until your phone switches off.
Press and hold the volume down key, and tap the power button briefly. Continue to hold the volume down key until you see a exclamation mark on the screen.
Your phone will reset itself to factory settings. Two cogs will be shown during this process, it may take some time to complete.
Your phone will restart and the interactive set-up process will begin, as if setting up a new phone.