I have mustang 2001 wont shift out of park , not able to push the button in on gear shift. It lock in park

For most any car that you find a SUDDEN problem where you can not get your car out of park, and had NO problem before (getting out of park), you can make it work (until you get it fixed) this way in an emergency;
1) Put key in ignition
2) Turn ONE notch (to unlock steering)
3) Push brake peddle down then press the release button on shift handle
4) Take out of park and put in neutral (car may roll so hold brake)
5) Start car, select your gear and be on your way
Remember, once you put it back in park, you must follow 1 through 5 again.
To fix problem, change your brake-light switch. This most likely will fix the problem. You see, most cars now-days combine the brake lights, safety neutral, and cruise control all into one switch, which is located along the arm extending above the rubber padded peddle you put your foot on to apply the brakes. If you can't replace the switch yourself, you can take it to a shop that knows how.

I had the same issue last year. Tore into the shift and found a cable that goes into a brake pedal interlock way up under the dash. This was worn down and was not working. I took it apart and decided being able to leave my garage was more important than having the brake interlock. Works fine without it!

Detemp ball/button could be broke check the brake linkage/switch to the trans if not any of those block the tires start it and have someone get in and hold the brake then get under it and see if you can move the linkage.