What to do when your iPod is frozen:
Occasionally, iPods will get stuck, either while playing a song, or during turn on.  The first thing to try is the Hard Reset buttons which, if the iPod is accepting input will force it to do a full reboot. In most cases, the freeze is a one-time issue, and this solution will get you out of the situation.
Hard reset/Diagnostic/Disk Mode for various iPod generations
If the iPod reboots and is still stuck, try resetting it again and hold the Disk Mode buttons to force the iPod into disk mode (it will appear as an external hard drive). Initiate iTunes and see if it is recognized; iTunes may recommend re-installing the software.  Restore is one  way to get your iPod working again.
If these fail, and you are willing, you can do the brute force method, which surprisingly works much of the time.  The iPod is, at its core, a hard drive, and sometimes the hard drive gets stuck.  To unstick it, you will need to apply a jolt (do not do this while the HD is spinning).  A mousepad is a good surface, because it buffers the blow a bit.  That's right.  Bang it a bit to unstick it.  You may want to try this with increasing amounts of impact to be sure you don't overdo it.  One person threw it over their shoulder in disgust, and that did it (but it would seem that falling from 5 feet in the air is a bit much for a hard drive).