Here is my video card Sapphire HD 6850 PCIE Video Card (100315L)
Using the 2 DVI outputs on the video card and one the motherboard, I tried to connect 3 monitors to my Windows 7 PC, but the 3rd one is always coming up blank.
How do I begin to troubleshoot whatever is wrong here?
It should work on Windows 7. Multiple monitors controlled by different drivers is officially supported.
Does each port work by itself? If the motherboard port doesn't work under any circumstances, the most likely issue is that the port is disabled in the BIOS. You'll need to enable it in the BIOS and make sure it has a driver installed.
You'll be a lot happier, and get much better performance, if you get an HDMI-to-DVI adapter and connect all three monitors to your video card.
Many motherboards don't allow both integrated (on-board) and discrete (card) video controllers to be used at the same time.
You may want to check the support resources from your motherboard's manufacturer to confirm or deny this ability with your specific model.
HDMI to DVI uses a passive adapter or cable. Use such an adapter or cable to connect the third DVI monitor to the HDMI port on the graphics card. As already mentioned the integrated graphics is often disabled when you use a discrete graphics card.
