I think people try to offer suggestions that nobody else offered just to cover all the bases. It is not a competition to see who is right. Take a few deep breaths - look at your manual and see what you see. Start with checking your needle for being in correctly. Then re-thread the machine following the directions perfectly. Clean out the bobbin area - while you are in there, pull out the hook and check it for burrs and make sure it isn't broken - then see if it lines up behind the needle. Then take the bobbin case tension spring apart and clean the lint out of it and re-assemble. There can also be dried up oil on a thread guide or in the tension. Check the tension adjustment - is it is too tight or too loose. If you see excess lint or dried up oil in the tension you can clean and rebuild it. It isn't rocket science but some times when the machine is acting up it sure feels like it. Also you don't lose if you have to take it somewhere and get help. You still win if they can fix the machine. It is a matter of what you feel comfortable doing.