請教：雙顯卡4顯示器

I got a Asus PN5D 2-SLI motherboard, two asus X500 PCIE video card (I do not want to bridge them to make them work as one, they are not sli ready) my question is, can I use them to support 4 monitors? So far windows can not detect the video card on the second PCIE slot, I tried different things and nothing worked, please help