LG G3 reset to factory settings using the keys:

LG G3 can not open your device, or you can not access the phone settings, using the hardware buttons on the LG G3, you can reset your phone to factory settings.

Turn off your phone.
Volume on the back side of your phone while in the closed position while holding down the Power Down key (Power) Press.

opening the phone, the LG logo appears when On (Power) button to remove your finger.

Finger pulled back immediately after Power (Power) to continue to press.

When FACTORY HARD RESET under the title Erase all user data & restore the default font settings to be hovering over the button Yes Volume Down, Power (Power) Press.
When the query again come out on the Yes button Down Volume, On (Power) Press.

LG G3 format, launching process began. Your phone will be reset to factory settings when the transaction is completed.