I returned my iPod to Apple for just this reason. After three days of use on a new iPod, it froze at then end of a song and that was it. It would not reboot. Following all of Apple's knowledge base suggestions did not work. In my case it needed to be replaced. I would, however, go through the 'wont wake from sleep FAQ' in the Apple iPod knowledge base. Not all things that lead to this problem are permanent.