Good advise from BAWS. Also make sure the saftey lanyard is connected fully and that the clip hasn't bent or broken.
I had a 89 190 TriStar that the ignition switch just quit working one day. Try turning the key and giggling it a bit and see if anything starts to work or if the starter kicks in a bit.
I'm sure JimN could provide better dianogistic help but this is quick and easy.