Configure X - 1'st stumbling steps

On Ubuntu, your X is probably not configured properly from the beginning.

Check in /etc/X11/xorg.conf
Section "Device"
        Identifier      "Whattever"       
        Driver          "i810"                   <-- Might say VESA or something else default

Also check that your driver is really installed on your system:

ls /usr/lib/xorg/modules/drivers/
:
i810_drv.so
:

(Change "i810" above to whatever is apropriate for your system, nvidia e.t.a.)