Take some unwaxed dental floss and run it through the threading mechanism as if you were going to thread the machine--not through the needle..then pull the dental floss back and forth several times and then pull it out. A piece of thread may be caught in the machine and the dental floss can help to dislodge it. Do not use waxed floss. Also, the bobbin area may be full of lint and if the bobbin does not spin properly then it will cause problems with the upper thread. Remove the bobbin holder and clean out any lint with a brush or vacuum. Good luck!!!