I changed the battery on my ipod nano and now it

you reset settings in settings section in the i pod If you forgot the code:
Plug your Ipod into a computer (Dock or Cord)
Access your iPod, find a way to see hidden files (in windows you can via file options, mac... i don't know)
Once you can see a folder called "iPod_Control" enter it

Next you will see a folder called "Devices" Delete it.

Eject your iPod, once you start it up, it will ask you what language you prefer. ohh, and if you put your iPod back in your computer, and go back to iPod_control the folder devices is restored.

Last step, go to screen lock, and put in a new password (or just leave it blank)

Your songs and playlists are still intact :D :D

I hope this helps and good luck. Please vote and leave a message.