So I had a MPCS Optimus F6 on 12b charged and powered off sitting in the drawer for about two months. It now won't power on at all. The LED button doesn't light up when connected to the charger. The battery measures 4.2v so it's fully charged. I put a working battery from my other F6 into the phone and it still won't turn on. Is there anything I can do to revive it? I've left the battery out for several hours and it still wouldn't turn on. It was definitely still working before I turned it off and packed it away.