endgate liftgate won't release from either button

I have a 2000 gmc jimmy.80K miles. The endgate that has a window in the top half and a tailgate in the bottom half of it.
I press the button inside the car to release the window and I the noise is made but the latch doesn't move and release the window. This happen with the button on the outside of the liftgate also.
Noise but it stays unlatched.
Any ideas as to a common problem with this?Thanks for your time!