Is there a piece of thread stuck in the tension discs? It might be the spool of thread, try a different one and see if that helps. With the bobbin thread being able to be pulled right out, it seems like the top thread is being pulled to the back. Is there too much tension in your bobbin? Can the bobbin case be adjusted? On my Bernina there is a tiny screw and it goes tighty righty or lefty lousy.