The device appears to be dead even when connected to the AC/DC adapter
There are a few possibilities as follows:
The PLAY key was not pressed and held long enough. To power up the unit, press and hold the key until the display turns on.
The battery of the hdd is not charged. When you use the GoGear, always make sure that battery is charged sufficiently. (It will take approximately 4 hours to fully recharge the build-in battery of your hdd). IMPORTANT: When using your GoGear for the first time, please make sure that you have charged the GoGear for at least 4 hours to let the battery build up the required operating voltage before use.
The GoGear is hanging up. Connect your GoGear to the AC/DC adapter, do a soft reset by pressing and holding the and the volume + keys at the same time for a couple of seconds, then switch on the Jukebox normally with the button.