While the AC is connected, I shut down the PB, and when trying to restart the unit doesn't respond and the AC plug light goes out. I unplug and replug it and push the power button and sometimes it will start and sometimes it won't. When it finally does start, the clock is reset to 1969 and the battery is depleted. And I usually do this when the battery was fully charged before. Is my PB defective or is shutting down an issue? Any input would really help.