Under the cabinet you'll most likely find a cord block with two outlets in it. One will be marked "light" and the other "motor". One cord will come out each end. The end with the light outlet will go to the wall outlet, the other to the knee controller.
Either the motor and light cords are unplugged, or there is a broken wire in the cord set. Use a regular extension cord and plug in the light first. If it doesn't light up, check the bulb. Then 'briefly' plug in the motor. It should take off like a banshie. That will tell you where the problem is. Machine, or cord block.
Joe