are you doing Free motion quilting or regular quilting??
if FMQ you need to lower your feed dogs but dont' forget when you start sewing to make sure your needle shaft/foot lever is in the down position. it's easy to forget and that will definitely cause a mess underneath.
Ah, re-read your post. I would rethread the top and remove the bobbin and clean your machine well. then reinsert your bobbin and try again. sometimes it's just as simple as fuzz that needs to be removed.