I had a similar problem --- I uploaded 5000+ songs to Google Music but couldn't get them to show up in Google Music, even though my account was set to sync and had done "refresh" several times via Google Music settings and even power cycled twice.
The cure? Uninstalling Google Music and then reinstalling.
Suddenly every thing is working great! Am now listening to my online library! Awesome!
Now to see if I can get the Bluetooth to work with the radio in my Toyota Corolla. Fingers crossed.
So the lesson learned, at least for me, is have content to