According to Apple Computers, the maker of iPod Nano, most problems you run into while using the device can be resolved simply by restoring the device to manufacturer settings. When you restore the iPod Nano, it will revert to the settings it had when it originally shipped, before you installed any songs, pictures or other files on the device. If for whatever reason you cannot hook the iPod Nano to a computer, you can restore it without the computer, using only the controls on the device.
Plug the iPod Nano into its power cord and charge the device. If you do not have the power cord, you can dock it on speakers or any other device that will charge the Nano.
Flip the "Hold" switch on the top of the device so the Nano is unlocked. A strip of white colour will be exposed next to the switch when the iPod is unlocked, instead of orange which indicates that the device is locked.
Hold down the Nano's "Menu" portion of the selector wheel, as well as the button in the middle of the wheel. Let go of both buttons after about six seconds, when the Apple logo appears on the Nano's screen.
Wait for the Nano to reboot completely. The device is now restored and ready for you to use.