This is just a guess on my part. Make sure it threaded right, that the thread isn't caught anyplace, put a new needle in and make sure it's in right. Tighten the bobbin back up to where it's close to where you started. Loosen the top tension maybe back it all the way off and slowly tighten the top tension sew some and see how it looks and keep adjusting the top tension. If their is more than one place to adjust the top tension adjust them at the same time. Just about every time i had had problems like yours it was because tension was to tight. Maybe somebody that really knows will come by.