If you've got a 6th generation nano, try this article for instructions on resetting it.
Even though it doesn't look much like a desktop or laptop, the iPod nano is essentially a small computer. And, just like a regular computer, sometimes it needs to be restarted. If you've got a frozen iPod nano that isn't responding to clicks, it probably needs a restart the same way a desktop computer would. Luckily, it's easy to reset an iPod nano. Here’s how.
NOTE: This works for the following models:
NOTE: First make sure that your iPod's hold button isn't on. This is the little switch at the top left corner of the iPod nano that you can move to "lock" the iPod's buttons. If it's turned on, you’ll see a little orange area at the top of the iPod nano and a lock icon on its screen. This could be causing your nano not to respond to clicks.
If you see either of these, move the switch back and see if this fixes the problem. If it doesn't, do the following:
Slide the hold switch to the on position and then move it back to off.
Hold down the Menu button on the clickwheel and the center button at the same time. Press them for 6-10 seconds. This should reset the iPod nano. You'll know the nano is restarting when the screen darkens and then the Apple logo appears.
If this doesn't work the first time, repeat the steps and try resetting the nano again.
If a second or third reset doesn't solve your problem, try plugging your iPod nano into a power source (your computer or wall outlet) and let it charge. Then repeat the steps.
If after all this, your nano still doesn't work, you may have a bigger problem, and ought to contact Apple to get more help.