ipod classic fully charged shows black screen when disconnected from USB

I have an ipod classic a few years old, and I didn´t use it for some time. I connected it to my MAC to charge and add podcasts, updates... All seams well and works fine until I disconnect it, it then goes into a black screen like it is totally drained for batteries. It is not possible to reset when it is not connected to the MAC or power source.

I also charged it through the battery loader, but the same problem: screen shows fully loaded, everything works well when connected to power, but black screen shows up when I disconnect.

Any solutions?

Thank you!