Have tried running your system outside the case? The method is called "breadboarding" and you set your motherboard on a flat piece of cardboard (to keep it insulated), on a tabletop. Then you install the components to the board, connect the power/data/video leads to their components, and fire it up. If you try this and your card works, then it is likely your new case is causing a short circuit, or other problem causing the video card to fail. Just keep children, pets, and metal objects away from the setup while you are testing it.