Have you tried a re-set. Switch the lock on and then off. Then hold down at the same time the middle button and either the control at noon on the dial or the control at 6 on the dial (I always forget which). This will re-boot the iPod.
If that doesn't work, plug it in to your computer and on the iTunes Summary tab, choose to restore your iPod (first make sure all your music is on your computer b/c this will erase and re-set the unit).
If that doesn't work, call Apple support.
