I had the same situation after changing the bios settings as you described.
Originally Posted by FunnyLookinHat
I found the following in /var/log/Xorg.0.log
Then, I removed all nvidia-173 packages (which I had installed for trying out older drivers) and reinstalled nvidia-current, ran nvidia-xconfig, rebooted and now everything works as it should.
[ 18.940] (EE) NVIDIA(0): The NVIDIA GPU at PCI:1:0:0 is not supported by the 173.14.30
[ 18.940] (EE) NVIDIA(0): NVIDIA driver.
[ 18.940] (EE) NVIDIA(0): Failed to initialize the NVIDIA graphics device!
[ 18.940] (EE) Screen(s) found, but none have a usable configuration.
Fatal server error:
[ 18.940] no screens found
My current nvidia driver version is 270.41.06.