DO the brake lights work?
trans fluid is half full on dip stick
There is a solenoid that allows the shifter to come out of park. If this solenoid is not getting power or this solenoid is not getting a signal from the brake light switch, this solenoid will not activate.
There is a 2o amp fuse that supplies power to this solenoid. Lets start by checking this fuse to be sure its good.
Well, that should not cause the shifter to "not" come out of park.
If you were low on trans fluid, then it would go in drive but the trans would slip.