Mac Pro 2010 Graphics Card Upgrade Help

So I have a Mac Pro 2010 with a upgraded a CPU (6-core Xeon 3.33 GHz) and I want to upgrade the graphics card to RX 480 (It is fully functioning, I put it in my windows computer to check). So when I do change out the graphics card and connect the display through HDMI, the display show that it detects no input signal. So I was wondering what it is going on. My Mac Pro is updated to Mac OS High Sierra. Do I have to change some programing function to add RX 480? Also I got a dual 6 pin to 8 pin cable to connect to the MSI RX 480 8GB.