When I turned on my garmin 840 after 2 weeks it had 87% battery left and an update started via wifi, I plugged the unit into the usb charger and it began flashing, no charging showing. It didn't connect to garmin express. I turned device off and back on, same thing. I turned computer off and back on, same thing. I removed device from garmin express, and then plugged back in, garmin express could not find unit. I left plugged in over night, battery is drained and is at 0%. What happened?