The bobbin housing has to be in exactly the right place. You may have bumped it. I doubt it would move that easy but you never know. There is a notch where the case has to fit in right underneath the needle. And be sure the bobbin thread is pulled to the right outlet on the bobbin. Sometimes my bobbin thread will come out of the slot. This happened on a Featherweight at guild too, we all tried different things with it and it was the needle was backwards. Remember everything on a Featherwieght goes to the left. The flat of the needle to to the left, and threading the needle goes right to left.