You do not appear to be using the NVIDIA X driver. Please edit your X configuration file (just run `nvidia-xconfig` as root), and restart the X server.
って怒られて、じゃあnvidia-xconfigを実行してみたら、
Using X configuration file: "/etc/X11/xorg.conf".
VALIDATION ERROR: Data incomplete in file /etc/X11/xorg.conf. Device section "Default Device" must have a Driver line.
Backed up file '/etc/X11/xorg.conf' as '/etc/X11/xorg.conf.backup' New X configuration file written to '/etc/X11/xorg.conf'