Hello Anne, If you have taken the needle plate off at any time make sure it is back on correctly, make sure you have enough pressure on the presser foot, with the teeth up and the foot down you should not be able to pull the material through, make sure the teeth are coming up just above the needle plate, finally make sure you are not sewing on something like satin unless you have tissue paper on top or the proper foot.
drivewithken, January 2010