My nano will not power on when fully charged, screen remains black.

Bought early 2012, no idea what generation it is. When connected to the stereo, the screen illuminates and nano works with stereo controls. When I try to take the nano for a run, when holding the power button down the screen remains black and no amount of touching the screen will produce an image or any sound. Any ideas about troubleshooting the black screen when powering up un-connected?