If your iPod 4th Generation locks, crashes or freezes up completely you need to reboot it. That is easy to do just by holding down the top right button and the Home button at the same time. While you are holding these buttons down, allow the slider to turn off prompt to appear and then disappear. At this point your screen will go black and your iPod will begin to restart. Keep holding down the button on the top right until the Apple logo appears on your screen, then release the button and let your iPod finish booting back up.  It should then operate normally. If it freezes up or crashes again, repeat the process and also make sure it is fully charged.

Source Ipod About