I would suggest rethread the machine also take bobbin out check it and put it back in pull bobbin thread to top now pull just bobbin thread does it feel right??? not like it is tugging or too tight, okay now put practice piece on frame and stich a few stitches do you see the bottom thread??? if not increase the tension on top until you do see bobbin thread after stiching when this happens you can back off the top tension so you don't see it on top again. Do this adjusting tension a little at a time hope this helps you if it is a practice piece you won't have to rip out.