You should try first with a reset.
In detail from the site:
To reset iPod nano try Step #1 or Step #2:
1. Press the Sleep/Wake button and the Volume Down button for at least 8 seconds until the Apple logo appears. You may need to repeat this step.
2. From the Home screen on the device, tap Settings then:
Tap Reset Settings.
Tap your language, then tap Done.
If the above steps did not work, try connecting iPod to a power adapter and plug the power adapter into an electrical outlet, or connect iPod to your computer. Make sure the computer is turned on and isn't set to go to sleep. Try resetting the iPod while it is connected to power.
Of course, you'll have to put all your music and pictures back.