most likely you broke the female end of the plug, is a very small plastic part that the plug fits into. You will need to replace that part. If you machine is older you may have a hard time finding a replacement part for it. You may need a tech or electrician to pull the wires out, and wire in a retrofitted plug if you cannot find one for your machine.
You can try www.fitnessrepairparts.com or www.treadmilldoctor.com for parts
You will need to full model # of the machine, its usually located by the floor on a sticker on the frame of the machine. Sometimes you need to tip the machine on its side to see it, it may be on the bottom of the frame facing the floor.