You must have a fray/short some place in your cord. I'm sure it can be fixed. :)

This same thing has happened to me before. I discovered dust around the button on the foot pedal. I cleaned it out and put a drop of oil on each side of the button. I sometimes think they have a mind of their own.

Well hubby cleaned the connections and removed all the lint and thread that collected in the foot pedal. Everything worked great for about an hour then it went crazy again. I'm pretty sure it's something in the connection plug into the machine if it wiggles slightly the machine starts going