Those button style foot pedals can go bad on you pretty quickly. Can you beg, borrow, or steal a newer type to try with it? That would be a quick check, and if that doesn't work you can go on to the next possibility. Have you checked for thread wrapped around the hand wheel, spool pin, and bobbin area? FWs don't like even a tiny bit of excess thread around the bobbin. When I got mine it didn't work well - finally found a 1/3" piece of invisible thread caught up behind the bobbin and fixed the problem.