My ipod nano is not working so I can fomat it
Plug into your computer.
Boot up itunes.
After the device is connected, use the itunes "restore device to factory defaults".
That will wipe the hard drive of the ipod nano and enable you to start using it again. IF it doesn't work, you'll need to contact apple support for more assistance. However, 99% of the time, the factory restore in itunes will solve the problem.