My machine had this same problem a few months ago. I learned I needed to "reset" the top tension. What this means: put the needle in the top position (my knob has markings to match this up right), then rethread your machine. If you put the foot down and pull on the top thread, it should prevent you from continuously pulling. If it does this, the top tension is fixed, and your problem should be fixed.
Every time I open the fridge, the hole in my jello glares at me.
Thank you for completely removing my signature without emailing me that it was too long.