I hosed the nvidia configuration on my linux box when I tried to set up a second monitor. I kept trying to fix things by reinistalling the driver and running “nvidia-xconfig” like a prompt in nvidia-settings told me. But each time I tried to run nvidia-settings, it told me that it did not appear I had the nvidia driver loaded. When I needed to do was run “sudo nvidia-xconfig”, then run “sudo nvidia-settings”. Once everything was set up, I was able to save the new configuration file (since I was su now).