By chance, did you recently remove the needle plate to clean out lint? Try removing the needle plate, then lift the bed extension up to access the bobbin case. Take the bobbin case out, then make sure that the knob on the circular "bobbin housing" ( not really sure what this is called) is in the upright position and put the needle plate back in place. The housing should not move if it is in the proper position. Replace the bobbin case. This did the trick for me. Good Luck Holly