Have you tried restarting or resetting your iPod?
Restart: Press On/Off button until the Slide to Power Off slider appears, select Slide to Power Off and, after the iPod shuts down, then press the On/Off button until the Apple logo appears.
Reset: Press the Home and On/Off buttons at the same time and hold them until the Apple logo appears (about 10 seconds). Ignore the "Slide to power off"
If these don't work you should try restoring your iPod using iTunes on your computer