Then press and hold the Power/Lock key + Volume Down key + Home key.
Now when the LG Logo appears on the screen, release all keys.
Make sure, that your phone is on.
Now from the Home screen, touch -> Apps tab -> Settings -> Personal -> Backup & reset -> Factory data reset.
* Note that this procedures reset your settings to the factory default values and delete all your data.
If you reset the phone this way, you are prompted to re-enter the same information as when you first started Android.
Turn off your device.
Next press and hold Volume Down, and plug in you USB cable into your phone and PC.
Then press the Home key until you see Adnroid green man.
* You can see what you must to do in video, which contains this tutorial.
Now if you see logo LG, then release holded button, and plug out USB cable.