You may need to change the battery, see other answers but try a factory reset, while keeping it on the charger press and hold the side button for a minute or so until you see the LG logo then let go, it may then do a reboot. If not - when you get the LG logo swipe from 11 to 3 and you may get a 'bios screen' at that point press the 0 symbol at the bottom of the screen. Odds on it will require a replacement battery I think.