Sometimes it can be as simple as not completely plugged in.
This article shows how the iPod should appear:
If it is plugged in, make sure you have iTunes 10.
You can check to see if you have updates in iTunes by going to Help > Check for Updates
You also want to be sure you are connected to a USB 2.0 port
Sometimes on a desktop the front ports leech from the back and become only 1.1 USB, so always check the back ports.
If these do not work you can always check the steps in this article to see if any of these solutions help.
Hope this helps!