I Got a msi b85-g43 gaming, and the 8 pin is for my motherboard, and i put the cabel in the motherboard. Because i did not install the driver for my motherboard
Which cable are you talking about, the HDMI?
Do you have a video card on this board? If you do, and you plugged into the motherboard, you won't get any signal out of that because the motherboard shuts those ports off to output from the video card, that could be what is happening as far as video.F
For your 8 pin, I had a similar issue a while back and the motherboard wouldn't boot unless I had the 24 pin and 8 pin plugged in on the board. Your power supply should have an extra 8 pin, if not you could get an adapter and use other power plugs on your harness that are free to power the board.