Several things could keep iPod from appearing in iTunes or in the Finder when you connect it to your Mac. The most likely causes are listed below in logical order (you'll find information for both USB and FireWire iPod connections). Check each one starting from the top of the list to see if that is what's keeping iPod from appearing.
Try to Reset, Retry, Restart, Reinstall , Restore <=== One of these might help you with your problem.
1 - Simultaneously press the top button + home (central) button.
2 - Keep both buttons until the Apple appears.
3 - Then release only the top button but still hold the home button pressed.
4 - The iPod goes into recovery mode and then you can restore it via iTunes