My system has been behaving fine up until I went into Nvidia X Server
Settings, and got a message"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."

So I did, and terminal displayed a message about how no xorg.conf file
exists, and it created one at /etc/X11.

Now when I boot, I get a message about how Ubuntu is running in low
graphics mode. There are a number of choices, and if I pick "restart X"
I can boot up. I have these in my /var/log:
Nov 16 20:08:37 bruce-desktop kernel: [ 10.420492] nvidia
0000:01:00.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16
Nov 16 20:08:37 bruce-desktop kernel: [ 10.420506] vgaarb: device
changed decodes: PCI:0000:01:00.0,olddecodes=io+mem,decodes=none:owns=io+mem
Nov 16 20:08:37 bruce-desktop kernel: [ 10.420694] NVRM: loading
NVIDIA Linux x86_64 Kernel Module 96.43.17 Thu Apr 15 14:49:01 PDT 2010
Nov 16 20:08:37 bruce-desktop kernel: [ 10.708336] NVRM: RmInitAdapter
failed! (0x23:0xffffffff:684)

And this in xorg.5.log:
(**) NVIDIA(0): Depth 24, (--) framebuffer bpp 32
(==) NVIDIA(0): RGB weight 888
(==) NVIDIA(0): Default visual is TrueColor
(==) NVIDIA(0): Using gamma correction (1.0, 1.0, 1.0)
(**) NVIDIA(0): Enabling RENDER acceleration
(II) NVIDIA(0): Support for GLX with the Damage and Composite X
extensions is
(II) NVIDIA(0): enabled.
(EE) NVIDIA(0): Failed to initialize the NVIDIA graphics device PCI:1:0:0.
(EE) NVIDIA(0): Please see the COMMON PROBLEMS section in the README for
(EE) NVIDIA(0): additional information.
(EE) NVIDIA(0): Failed to initialize the NVIDIA graphics device!
(EE) NVIDIA(0): *** Aborting ***
(II) UnloadModule: "nvidia"
(II) UnloadModule: "fb"
(EE) Screen(s) found, but none have a usable configuration.

Fatal server error:
no screens found

How can I fix this?