4G Nano won't connect to Mac or iTunes

I have a 4th Gen 8gb iPod that works just fine, battery will hold a charge after a nights charging.. It plays the music that is on there just fine. Click wheel works just fine. I know that the cable it good, as it works fine with my 2nd gen. Basically everything works except there is no recognition by the Mac, iTunes, or the system info.

So I can do everything except connect it to my iMac to change out the music.

I have tried holding down various key combos looking for something different - but they all just boot up the iPad. I am not sure what key combo's to be using. Haven't found a clear description of what the combo's are and what they do.

I am getting to know these songs I can probably sing them backwards.

Any help greatly appreciated.