Here's how you can perform a hard reset the LG Optimus 3D P920.
If you device is not functioning correctly, or it has frozen and not responding at all then you coud try to reset it back to the factory settings.
Note: By peforming the below steps you will lose all data on your phone, so it is advisable that you backup any data that you wish to keep. here's how:
1. Go the Home screen.
2. Then select Menu.
3. Next select Settings.
4. Then select Privacy.
5. Next choose Factory Data Reset.
6. Then select Reset Phone. If you want to erase the SD card too then ensure the checkbox Erase SD card is ticked.
1. Switch off the phone by pulling out the battery and put it back in.
2. Press and hold the Home + Volume down button.
3. Press and hold on the Power button until you see the device switch on.
4. An on-screen instruction will appears and guide your through the rest of the process.
Once you have finish with the clean wipe, the device should startup fresh with all the default factory setting. You can now restore any data that you have from the backup.