I just installed nVidia GT440 w/ NVIDIA-Linux-x86_64-280.13.run driver on my Scientific Linux on two of my workstation and one of workstation sound disappeared.
Both workstations are identical though in terms of hardware and OS (Scientific Linux).
I'm not really sure where to look, but here is dmesg from workstation where sound isn't working: http://pastebin.com/tw29guqD
whenever I go to System -> Preference -> Sound -> Output on broken workstation I only see "HDA NVidia Digital Stereo (HDMI)" and my old/onboard sound card is missing.
I actually did roll out of same Video Card to more then just 2 workstation, I did that to a 5. Only 2 of them sound working as expected. 1 of them didn't even needed to install nVidia drivers but that workstation running slightly newer OS version 6.1 instead of rest 6.0, so I'm back to where I started it ... clueless ;(