I don't have a machine like yours but they all mess up the same way. If the bobbin thread is messed up it's usually the top thread that is wrong somewhere. Is your needle in backward? Are you threading it left to right or right to left? That will really mess up a stitch (took me hours to figure that out) Has little fingers been turning your tension dial? Maybe all the way around several time? (took me a few days to figure that one out) My bobbin winder wasn't all the way disengaged and the machine just wouldn't sew a seam no matter what I did. (took me several weeks to figure that one out).