The system is running in low-graphics mode (12.04)

I had the same issue from updating. It seemed like xorg broke from not having a config file. Nor can it be auto-generated so I copied the xorg.conf.failsafe and made a new xorg.conf. Let me know if that helps.

I notice you deleted that file. This is what mine looks like. I am working on get this auto generation to work though.

Section "Device"
   Identifier  "Configured Video Device"
   Driver      "fbdev"
EndSection

Section "Monitor"
   Identifier  "Configured Monitor"
EndSection

Section "Screen"
   Identifier  "Default Screen"
   Monitor     "Configured Monitor"
   Device      "Configured Video Device"
EndSection

@51

I also have an HP Compaq 4000 Pro SFF, running Ubuntu 12.04 LTS.

I just experienced the same issue ..

@Sam

I tried copying the missing xorg.conf file back from failsafe version, which appears to resolve.

eg.

[ login to text-mode eg. Ctrl-Alt-F1 ]

cd /etc/X11/
sudo cp xorg.conf.failsafe xorg.conf

sudo shutdown -r now

CLEANUP

1. What was the root cause?

2. What is the downside to adding ppa:ubuntu-x-swat/x-updates

3. What did I lose, from my old xorg.conf file?

UPDATE: 19-May-2013

from: @scott's answer to "the system is running in low graphics mode" I get this message when I boot my ubuntu

1. Don't attempt to restore missing xorg.conf file, as it is not needed.

   This is apparently an issue (bug?) with lightdm, which 'reacts badly' to the missing xorg.conf file.

2. REMOVE errant xorg.conf.failsafe file, to stop lightdm from making bad assumptions.

eg.

[ login to text-mode eg. Ctrl-Alt-F1 ]

cd /etc/X11/
sudo mv xorg.conf.failsafe xorg.conf.failsafe.safe

[ skip next line, if you are still missing this file ]
sudo rm xorg.conf

sudo shutdown -r now

UPDATE:

Intel driver unstable. Random logouts, desktop glitches.

Working to resolve ..

This simple fix removed the error completely on 2 machines with Intel graphics on Xenial (16.04):

1. sudo xdiagnose
2. Check "Disable bootloader graphics" in section "Workarounds"

From the docs:

The grub bootloader has a graphics mode using the VESA framebuffer driver which can sometimes interfere with later loading of the proper video driver. Checking this forces grub to use text mode only.

Please leave a comment if this works for you. Trying to solve this for 4 days straight and trying every suggestion out there I found this fix by accident.