96 Jimmy, rear window & tailgate won't open

I have a 1996 GMC Jimmy, the rear window and tailgate will not open, when you try to open it with the key or tailgate button I get a buzzing sound but the glass will not release, the same thing happens when you push the dash button. It will not open with the inside handle either. I can not get the panel off because the tailgate is closed and the panel screws are on the sides of the tailgate. How do I bypass the electric switch in order to release the glass and to drop the tailgate?