I'm guessing that there is a thermal fuse or link that is breaking contact once the machine overheats. When it cools down, the contacts are together again. Have you talked to the sewing machine repair guy to ask what would make it overheat? I would want to talk to him in person, asking a lot of questions, before making a decision. Is it possible that there is not enough ventilation, causing it to overheat?, perhaps a lint build-up inside the housing?