OSX does not support GTX 750. I have the same card and it wont work. There is a big chance this graphic card will never be supported. So ether replace or just forget about OSX for now. If you want to make it boot when you install it using niresh cd chose nvidia driver for non compatible graphic cards than try booting GraphicEnabler=no . It should work but you wont be able to do much without graphic acceleration. Good luck.