no sound at all ?
i would first try different headphones, if they won't work either, i would hard reset the iPod (press and hold the menu and the select button at the same time until the iPod restarts. you could also try to restore the iPod with itunes.
if everything won't work - it's most likely a hardware issue
starting from the [http://www.ifixit.com/iPod-Parts/iPod-Mini-Headphone-Jack/IF196-004|headphone jack] and ending with a faulty logic board.