Resetting an iPod should only be done if you cannot restart, but sometimes an iPod Touch simply freezes and there’s no other way. To reset, press and hold the Sleep/Wake button and the Home button simultaneously until you see the Apple logo. Be patient, because it will take at least 10 seconds to reset. Don’t perform a reset when your iPod Touch is connected to your computer; eject it before resetting. If you have a 6th generation iPod Touch, hold the Volume Down button instead of the Home button along with the Wake/Sleep button.
Restoring the iPod Touch - If you can't get it to restart by resetting, you can use iTunes to perform a Restore. First, make sure your iTunes is the latest version. If you are able, also perform sync to back up your data. Restoring your iPod will wipe all your data, so you will have to do a complete sync to get it back afterward. Connect your iPod to your computer's USB port and open iTunes. Find your device in the Source panel in iTunes. Go to the "Summary" tab and click "Restore iPod" and follow the on-screen instructions.
Forcing Recovery Mode - If you cannot get your computer to recognize your device, or your iPod fails to complete the Restore, try forcing your iPod Touch into recovery mode. Start with your iPod off. If you cannot shut it down, wait for it to run down and then charge to the level where it will turn on, or at least get to the Apple logo. Open iTunes and then press the iPod Home button while attaching the device to your computer and hold the button down until the "Connect to iTunes" message appears on the screen.