That's a bummer.  I hope your card has a good warranty.

Had the same thing happen to me, but with a 6870. I dos-booted off a USB drive to see if atiflash found the device. Sure enough, it was picked up. So from there I did the standard things. Reseated the card(don't underestimate vibrations from all of the fans in the rig). Then I flashed a different, but slightly underclocked bios(this will void the warranty, and may not even work.) Then tried a different pci-e slot. And lastly, I just swapped power cables to work off different rails.

Well, all that fiddling, and it eventually came up.   RMA first, if you still have that option. But if you flash the bios, be 100% sure that it's the right bios for the card, as revisions and reference cards can seem identical, when they aren't. Also understand that you're responsible for any/all damage.

Is your power supply high quality?  Sometimes the supply will go when a power supply is just on the edge from mining.

Try reinstalling the drivers for the card and see, but I'm afraid you might have botched your card. 
I burnt a few this way when GPU mining was viable.