The following procedure applies to factory reset the LG optimus L9 in all its varieties, P760, P768G, etc., directed to give effect to this procedure is to remove the unlock pattern or try to solve software problems, for example when the no phone ends up boot and stays stuck on LG logo.
procedure
Turn off the phone or remove the battery at least 10 seconds
Simultaneously press the following combination of buttons: Vol - Home & Ignition
Keep the keys pressed for 10 seconds or until the display shows an android, that will indicate that the phone is rebooting (full reset).
Wait at least a couple of minutes until the phone turns itself off after that long to turn on the phone it is important not to interrupt the proceedings as it may damage the device.