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 (see image below) for at least ten seconds, until the Apple logo appears on the screen.

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Reset iPod – follow instructions here according to your iPod version.