Help? My new iMac won't talk to my old Nano6.

Help? My new iMac won't talk to my old Nano6. Now my music is GONE on the Nano (still in the Cloud). Says it's syncing, but nothing changes. I've done the "thing" where you click on the on/off button and volumn button until the Apple appears... that didn't work. I've changed USB ports with the cable. That didn't work.

Any ideas? I don't see my Nano listed as a "source" anywhere (I read that on another users question), but it is there when I connect... and it just keeps showing that there is no music on it and all of it's memory is available (I've not used it for anything other than music in our car).

Help please? The thought of having to listen to the radio as I drive is not a pleasant one!