iPod Nano froze up - how to re-boot?

Mrs Piper was listening to her iPod Nano in a docking station. When she took it out, it sort of flickered and now it’s frozen on the menu that was showing when she took it out. Doesn’t dim after the normal time-out, and neither the wheel nor the button do anything.

How do I re-boot it?

Thanks.

Apple on How to reset iPod

My nano recently froze up on me, and with no buttons working, it’s hard to follow Apple’s advice anyway.
I let the batteries drain overnight, not that there was any way to turn the thing off, and then pugged back into my computer. After a few minutes the iPod showed up in iTunes and I was able to reset it to factory specs through iTunes. It’s worked fine since.

I followed the instructions on that Apple link and it worked! Thanks, Squink!