Wait for it the battery to drain. My ipod nano did that to me a lot and I either restarted it or let the battery drain. It should come back up regularly when you charge it. Of course, my solution was to go out and get an ipod touch...but the best thing to do is drain the battery. Of course that means you wont be able listen to it for a couple hours. That makes this a perfect time to test how long the battery lasts, for future references!
Connect it to your computer.
Then reset it.
You may have to resynch your music library to the ipod after this but it will work. If it doesn't reset properly the first time, try it a few more times, as this is the "solved" solution that apple shows on their support area.How to unlock my iPod Nano when it's frozen?