Put in a different bobbin, sounds a bit like a thread lock if it sews in the same place all the time. Rethread your machine even if it sounds stupid and check for lint in your thread tension area, something is jammed. Checking the stitch length could be a problem too,like the precious quilter mentioned. Another thing, is the bobbin set in properly?
We are full of suggestions today, aren't we? Too bad one of us can't run over to your house and help you.
Carol J.