My ipod nano 4th gen (8Gb) froze "on". I couldn't switch it off or do anything with it. Took it back to the shop & the guy there held menu + centre button for several seconds. This cleared it and restarted/re-booted the ipod and I've had no trouble sinse. I don't know if this will work for you, but might be worth a try maybe?
Cheers.
Richie Rich, February 2009
