This happened to me when my phone died on paranoid android. As long as your on a custom rom you can boot into recovery by turning the phone on and alternating between both volume buttons. Unplug the phone and plug it back in wait a minute and hold power until the phone vibrates and you see the lg logo then alternate volume buttons and flash a stock rom like collab and it will charge with the battery indicator while off, be careful and don't unplug during the flash. the phone wont power on unless all three hw key lights are on so if the home light isn't on then unplug and plug back in and press power.