I rented a cadillac escalade recently and couldn't go on my trip because it wouldn't start for me. I tried everything that you tried. I called my roadside assistance and they tried. The rental company sent a tow truck and they tried. No one could figure it out. Until we talked to the dealership. It had something to do with the valet key. once they got a hold of the regular key, it started right up. Is it possible you are using the extra key(valet key)? In fact, you should have two regular keys and one valet/service key.