what to do if the device doesn't shows up in Finder (if on disk mode) or in iTunes?

I have a 3rd gen 4GB iPod Nano.

It just displays the Apple logo (even after resetting). If I activate the disk mode it says "OK to disconnect" but nothing happens if I plug/unplug it on my MacBook (with or without iTunes 11 opened).

I'd like to completely restore it ... but I can't. So far no article in the Apple KB has helped me ...

TIA