Hold the middle button and the menu button until it force resets.

Worst case you could hook it up to iTunes and do a restore.

if its an iphone or ipod touch just hold down the home button and the lock button untill it restarts.

If resetting it doesn’t work, just let the battery run down. I had to do that once, iTunes wouldn’t recognize it, it wouldn’t reset, so I let it die and plugged it in – problem solved. never happened again.

ok thanks guys!

Check out

http://www.command-tab.com/2006/03/31/fixing-a-frozen-ipod/

and

http://www.command-tab.com/2006/03/30/hidden-ipod-commands/

Hold the Menu and the Center button together at the same time until the Apple Symbol appears. Make sure the ipod is not locked.