How to hard reset Nokia Lumia 620, Lumia 920, 925, 928 and Lumia 820, 620, 520 and 720.
It is inevitable that there will come a time when you will need to perform a soft reset to fix minor issues within your phone. Both the Nokia Lumia 520, 620, 720 and Nokia Lumia 820 arrive with removable batteries as does the earlier Lumia devices (710 and 610). Removable batteries provide a quick and simple method to soft reset your phone by removing the back cover from your phone, removing the battery and then replacing the battery and the back cover, and restart your phone.
However, the Nokia Lumia 920, 925 and 928 and earlier Lumia devices (800 and 900) arrive with a unibody. This means that the phone is sealed with no access to remove the battery. To soft reset your phone, the instructions are as follows: [The Nokia Lumia 920 uses the same button layout as does other Nokia Lumia devices and the soft reset is demonstrated here on a Nokia Lumia 800.]
Follow the instructions as shown on the image by holding down the Volume down and Power keys at the same time until the phone vibrates three times. The phone will restart and after a few seconds the Nokia logo will appear on your home screen.
There are times when your phone may have problems, which a soft reset will not fix. If you encounter this problem, you will need to hard reset your phone. Warning: Performing a hard reset will result in the loss of all data. You are advised to take regular backups of your data.
Step 1: Backup all your data
The Windows Phone operating system is automatically designed to create a backup of your contacts to your Microsoft account. You can also use the backup services of SkyDrive, Google and others.
Step 2: If the phone powers on and allows you access to your phone settings: select Settings > About > Reset your phone. [This will erase all your personal content and reset your phone to its factory setting.]
If the phone will not power on, follow the method below:
Step 3: Switch the phone off.
To perform a three-key hard reset , switch your phone off before completing the following task.
Step 4: Three (3) key reset
An alternative method to hard reset your phone is shown above. Press and hold down the Power, Volume Down and Camera keys at the same time. When the phone vibrates you can release the power key but continue to hold down the volume down and camera keys until the phone reboots to the start screen.
Note: Nokia has issued an additional set of instructions should the above method not work to reset your phone.