There is a electric plunger on them that will pull the shut off back it might be that it has went bad, I think I would check that first.
Do you here a click noise when you turn the key on?
I f you remove the passanger side cover and turn the key on you will see a lever push forward that is the electric kill switch shut the key off and see if it pulls back.
If it does not move back then chances are it is bad or does not have power going to it, you can unplug it and check for power with a test light.
Check it out and let us know.
One last question How old is your machine?