I have a thread on this going in the motherboard sections, but I thought I'd see if those that frequent the GPU section of the forums have heard of this issue before.
The short version of the story is this: I installed a secondary GPU (GTS 250) on my brand new P8Z77/TB Pro to use as a PhysX card to supplement my GTX 560 ti. I installed the secondary card with the primary GPU already in place and the system completely shut off. The secondary card was also NOT plugged into the PSU at this point. Right in the middle of the installation, I heard a pop go through my speakers. After I installed the second card, I booted into Windows to find that I could no longer play audio. All the hardware seems to be working fine, but no sound is coming out of my Line Out port in the back, nor the Headphones port up front.
I should mention that the EXACT SAME THING happened to me yesterday with a different board. I tried installing this card in the same fashion and wound up with no audio. The difference was that this time the board/OS no longer recognized any changes in audio inputs, whereas my current board/OS does recognize changes in audio inputs. There just isn't any audio output. I RMA'd the first board, bought a new one at a local retailer, and had the exact same issue the instant I put in the secondary card. The fact that it happened twice in a row makes freak accidents like static discharge unlikely.
I would blame the GTS250, but it works fine. I've been benchmarking with it - and without sound - all day, and, as I said before, it wasn't even plugged into the power supply when I placed it in the PCIE slot. A problem with the GPU is the only conclusion. But, what kind of GPU problem could affect the onboard audio chip like that? AFAIK, the onboard chip isn't even in line with any of the PCIE lanes...
Does anybody know what's going on here/had this problem themselves? It's kind of driving me up the wall.