Sounds like the starter solenoid. Do you hear a click or hear the starter? If not and you are sure the battery is good and charged, chances are the starter or the ignition switch is to blame. On that age of vehicle, my first guess would be the starter because the battery has probably been replaced.
Old trick, try tapping the starter (lightly!) with a hammer. If it starts right up, then the starter solenoid is bad.
