A Few Things...
Here's a few suggestions. But first, a question: did you use it with a PC previously? If so, there may be a problem with the disk format, which you can, of course, fix. On to the suggestions:
1. Restart your computer and try again.
2. Go into Applications:Utilities😀isk Utility, and see if the iPod shows up there. Perhaps you will see some sort of hard drive or fire wire disk there.
3. Perform a hard reset (or two). Look in your iPod's manual regarding how to do this.
Make sure you have your music backed up before you start tinkering with your iPod (i.e., don't do any of these things if your iPod hold all of your music and your hard drive holds none, but I highly doubt you are in such a situation).
Mike LaRiviere