I suddenly found my PBG4 not functioning today. I left it charging, and when I opened the screen, it didn't come off of the sleep mode. When I looked at the screen release LED, it wasn't flashing or turning on when I press power. What should I do next? Mine is still under warranty and I may purchase AppleCare soon to avoid another year of problems. Unit isn't powering up at all. Help? I pushed the battery indicator button, and the LEDs are not lighting up. Do you need battery power to start PBG4? Can the unit function without the battery?