I had this happen to me one time...

I felt the knob go limp on me. I pushed and pulled it up and down untill I heard a click. Then I got the door to open and I proceeded to pull the door panel off. The cause of this whole mess was a small plastic piece that connects the metal rod from locking mechanicism to the metal rod thats connected to the lock/unlock knob. There are 3 grooves on this plastic, one 2 are used. (You will understand what I mean if you look at the part). I just simply connected it to another groove and it works fine now.