If you own a Apple iPod, iPhone or iTouch you may encounter the rare  but irritating device freeze, there could be several reasons for such  freeze, the very first step you should take is to try and reset/restart  the device and see if it works, use the following method to reset your  apple devices:
- Reset iPhone & iTouch - Press and hold Sleep/Wake button and Home button at the same time  for at least ten seconds, until the Apple logo appears on the screen.
 
Reset iPod - follow instructions complete in here :
http://support.apple.com/kb/HT1320?viewlocale=en_US