Why could'nt I get the shifter to unlock so you could put the car in drive 2001 Saturn?

Why could'nt I get the shifter to unlock so you could put the car in drive 2001 Saturn?
I would suspect a neutral safety switch. This is a mechanism that prevents your car from being put into gear without your foot pressing down on the brake pedal. With the car running put your foot on the brake first, then try shifting into gear. It has to be done in that order or it wont go out of park. If you listen closely when you press on the brake "while in park" you may even be able to hear the single "click" sound in your shifter of the switch doing its work....if it's working. If you don't hear a click or feel a click in you shifting hand when you do this I would start there.