This is even more likely to be what I wrote above. The PC only uses either your mobo port or your graphics card port. If you plug into both, only one will show.
I looked up your card, it appears to have a DVI and an HDMI port on the card. This means that the VGA port you are plugging into is on the Mother board and not on the graphics card. Remove that cable, remove the adapter, plug into DVI and plug in the HDMI and it should work.