For people to be able to help you, we need to know your operating system and version (Windows XP, Vista, Mac OS X Leopard, etc.), your iPod model, and how you're connecting your iPod to your computer (USB 1.0, USB 2.0). In general, providing as much info as you can is a good idea when looking for help with technology issues.
I assume you're getting a recovery mode message from iTunes, and you're exactly followed the restore instructions described
here?