Sometimes your bobbin may have fouled up. Try putting your bobbin in again also. Remember to back your design up 10 or 20 stitches when your thread breaks so that you don't skip any stitches in your design.Once in awhile the thread just will not unwind off the spool correctly. I pull a length off and hold it in my hand. The thread's route now becomes spool, hand, machine, needle. That way I can tell if it is catching on the spool and pull it free if it needs it and it doesn't break. I hope I explained this sufficiently. Good luck.