Comment 8 for bug 573557

I have the same problem. ASUS P5N7A-VM MOBO with 8500GT vid card using "hybrid SLI."
I was first using the default driver, but I wanted a little more performance. The current nvidia driver worked fine right after installation. Today I started getting notice upon boot that I was running in "low graphics mode," and I could sometimes get X to load correctly if I rebooted a few times. I removed the current nvidia driver and rebooted. That's when the really crippling behavior started. I would see some text about the nouvea driver echoed on the screen, and then the boot process would halt with the machine hard-locked. In the BIOS, I disabled the PCI-E 8500GT and was able to make the machine boot. I tried different combos of BIOS settings (PCI-E card off and on) and drivers (173, current, and via running the script for the nividia installer). The best results that I had was a machine that would use the nvidia driver but would hard lock any time that I tried to stop gdm (logout, reboot, shutdown, gdm stop, etc).
I have now physically removed my second video card, removed all of the drivers, reinstalled the current nvidia driver from the repos, and everything is working well with one card.