Singers do have a habit of doing what your mashine has done if thread is stuck down under the bobbin case area. I would take out everything I could and look and also while it is apart as much as possible use your vacumm cleaner and suck it out even if you do not see anything. It could be the tiniest bit of thread stuck down in there. Do NOT use canned air to try to clean it out. That only pushes stuff further inside it. And Say a Prayer...God always helps me :)