Originally Posted by simplyme
Try re=threading your machine both top and bottom and then try again. This is what I do first.
I agree. It sounds like the top thread isn't seated in the tension disc correctly. Be sure the presser foot is UP. This opens the tension discs and allows the thread to go between them. Then when you put the presser foot down to sew, the correct tension is on the upper thread and won't ball up underneath.