When I push the "start/stop" or "needle up/down" buttons on the handle bar, the machine just takes off at an uncontrollable speed or goes at a surging speed (slow down, speed up, etc). Then the "start/stop" button doesn't work to stop the machine. I need to turn it off at the power supply. Any suggestions??? I have a "snow day" here in Michigan and hoped to get a lot of quilting done today. Ugh!!!!