Huskylock 435 will not stop overlocking

Question

I turned off the light on the Huskylock 435 overlocker and took my sewing into another room. It will still on at the switch but this is what I have done a hundred times. When I walked back in the room the overlocker was spewing out overlocked threads, it had suddenly come to 'life' at some stage while I was out of the room. Nothing was sitting on the peddle. Tryed putting the cord in two different power points and turing on the machine and it automatically stared overlocking on the fastest speed. The only way to stop the machine is to turn the switch off.