I'm planning to sell an old gpu which is an ASUS GT 630 (worked fine in my old setup last time i tried it) so I tried plugging it in my B450 motherboard to test it but the beep codes say that it does not detect any graphics card. I tried reseating it but that didn't work. I've searched google for answers but it just says the 4.0 backward compatibility with 3.0 nothing about 2.0. My mobo is fine and works well with newer gpu.