Hi, you might have stopped following this topic, or maybe you've solved it yourself, but I thought I'd post a solution anyhow. I had this problem when I first installed win8, same series of graphics cards too.
I'm guessing you also have switchable graphics cards, and this is probably the cause of the problem.
Reboot your computer and enter BIOS. Go to main, and change graphics from "Switchable" to "Discreet". This worked like a charm for me. I can now play games and use HDMI once more.
I really hope this helps for you too, as there seem to be absolutely no other solutions that works out there.