iPod 4th generation stuck on "do not disconnect"

Hi I have a 4th Generation iPod Click Wheel, for about a year it was stuck on the Sad iPod face, but I managed to get it off that and I plugged it in. It then froze on the screen. Do not disconnect. It spent like that for over an hour and eventually I unplugged it. Now it has frozen on that screen. What can I do.

Thanks,

Charlie