Pithos not fully launching

Hi,

Just about the first thing I did when I migrated from Windows to Ubuntu a few days ago was install Ptihos. It's great! But today, when I try to launch it, it only partially launches -- the frame of the app and the toolbar are there, but it doesn't populate with any songs -- that whole area is blank.

What should I do? Please be really specific as I'm only just learning my way around Ubuntu.

Thanks!