First, I would like to know if the light is on when you try to set your speed. It should be on first. It will not come on if it is off when you try to set your speed.
The other thing is that sometime the vaccume hose gets knocked off and that keeps it from working. Check under the hood and see if one of the hoses was knocked off.
If the light does not come on before you try to set your speed, check to see if a fuse has blown. Good luck.