I have found, on my phone anyway, that when you hold the volume down key and the power key it just sits there. I have to hold the buttons, let the power button go til I see the "LG" logo and hold the power button again. Then it gives me the factory reset screen. But you have to let go of the buttons as soon as you see this menu. Then you can hit power, hit power again, and it boots into recovery. Give that a try and see if it works.