my solution
I bought a refurb nano and had the same problem. UNPLUG the Nano at the bottom, then UNPLUG the USB 2.0 from your computer. Reattach the cord to the bottom of the Nano and then to the computer. Give it two seconds and it the lovely lil' colour screen should come to life. If it does not work then try it again. This worked for me.
Cheers,
t