One work-around is to navigate to your audio drive and try to open another session. That will bring up the option to save/don't save the session that is open(but minimized). At that point, you have a choice; save(or don't) and the open session will close and the next session will open, which should bring PT up again. Or cancel(instead of save) and your open session may still pop back up on the screen(this happens to me once in a while but I still have no idea what causes it)