1995 Chevrolet Van: Why doesn't my ignition engage?

1995 Chevrolet Van: Why doesn't my ignition engage? when I turn the key sometimes the ignition does not engage ,I then woul turn the ignition off and try again and after 1,2 or 3 times it would start,one day it stopped comepletely,i tried to jump start it to no avail,do the ignition switches gradually go out?