96 Buick very intermitent won't start

If you seen my name, this is the same car, another issue.
Intermitently, the car will not start. You turn the key and nothing.
I am going to check all the connections to the starter. I am also
taking a close look at the anti theft key. I have heard they can go
bad because of a poor connection. Two things have happen, car starts,
go somewhere, come out, car won't start. Another time, car started,
shifted from reverse to drive and stop. In each condition, the engine
does not turn at all, however, the lights and fans all work o.k.
Battery is not that old and the one time I saw this I was able to
measure the voltage and it looked good.
Thoughts?