97 jetta dashboard door lock switch/cd changer

My daughters Jetta will not lock using the central lock switch in middle of dash. I hear a sound coming from rear of car when pushed ,but doors do not lock. Any Ideas?

Also will be adding her sony cd changer.The car already has aftermarket cd player. Any problems I might run into?

Thanks in advance for helping!!

check the vacuum pump module in the left rear of the car behind the carpeting. Its in a styrofoam box, look if the yellow or white plastic line came off or broke