How do you manually start a key-ignition gokart?

I have a 8hp gokart that is not starting all of a sudden(this is a video of the gokart problem and the click noise it makes when trying to start http://www.youtube.com/watch?v=17R2z2fvi8s). It has a belt and a chain. The batterys at full charge and all the cables connected to the battery are fine. I've used a light probe to test the wires. When I connect the ground leed of the light probe to a bolt on the starter and touch the other leed to any wires running from the starter to the solenoid and battery and turn the key, the light only dims when turning the key. All the other wires light it up brightly, and this is so even when the battery is hooked up to a jumper. Does anyone know how to find out if it is a starter problem or if the engine is locked/seized? The gokart was running fine recently and suddenly stopped working. If theres another way to figure out the problem, please describe it to me I am not very mechanically inclined.