All my music is gone

If 1) the unit was in Auto Detect or MTP mode under Settings/USB Mode

   2)  the computer you plugged it into had WMP 10 or 11

      and 

   3) the music library in that computer’s WMP was empty

it might have automatically “synced” your Fuze to match what was on the computer: nada. 

The default setting in WMP is Auto-Synch. 

Solution for next time: Switch to MSC mode before you ever connect to another computer. And while you’re at it, transfer your albums via MSC–just drag-and-drop–rather than dealing with WMP if you can possibly avoid it. 

For what it’s worth, Music is not the only place the songs can be. They can be on the Fuze anywhere. But if it’s not showing them, and it did before, they are probably gone.