The power rear sunshade is electric. The electric motor that raises and lowers the shade is located under the rear hat shelf. You can try lightly tapping the motor with a rubber mallet by opening the trunk and striking the right side bottom of the rear shelf. Sometimes these motors get a "bad spot" in them. I've replaced it before, huge job, and not fun. Rear seat, C-pillar trim, all the rear headrests, rear shelf, etc. all has to come out, about 3 pages of instructions to R&R that motor. I think the motor alone is around $250 or so from MB if I remember right, its been awhile. You could easily check the switch and fuse, but its usually the motor that goes south. Good luck.