There are electical motors in the duck work. If they fail this condition will happen. The door for both sides is most likley stuck or the motor failed. This is a very common problem and the only way to know for sure is to try to access the areas in question and test for voltage when the controls are activated, Your going to have to remove most of the dash in order to do this. If you need instructions go to mitchell1diy online and all the diagnostic trouble tress will be available,