Why can't I shift my vehicle into gear?

Keep in mind I am fellow owner- Lincoln Navigator 2006 You may need to use the override. Anyone who forces the gear shift will break the cheap plastic inside :/ There is a safety sensor in the brake pedal. Might of been what what needed replaced. Hence works sometimes. Honesty with Lincoln's - they break and then work again... I rarely spring for a repair. Get In car. Press brake - listen for a click- turn on car. If it won't work remove the plates around the gear shift- (below ashtray) think of building a lego and work backwards- strangely easy. Use a flathead screwdriver and press down tabs to release covers. The shape is a rectangle- on top left there is an over ride button- hold it down- press brake try again. I broke my shifter and didn't want to pay for repair- I literally use a long paper clip to stab the hole on the shifter- Raise it up and it allows me to change gears. Best theft proof you could ask for.