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

Every time I boot I get the "The system is running in low-graphics mode" error.

The problem is similar to this one: "the system is running in low graphics mode" I get this message when I boot my ubuntu, but I don't think I can use the answer, because I do not have the same graphics card (mine is Intel).
I have searched Ask Ubuntu for a solution and tried some of the suggestions found here: How to fix "The system is running in low-graphics mode" error?.

I'm using an HP desktop with Ubuntu 12.04.

I have never had this problem before until about 12 hours ago. The only thing I can think of is that I had just installed about 35 updates via the update manager. The next time I switched on my computer I got the "The system is running in low-graphics mode" error.

Here is what I have tried:

• Switching to gdm
• After realising that I had used almost all my disk space I freed some by deleting a lot of movies and then rebooting.
• Reinstalling ubuntu-desktop
• Someone suggested editing the LightDM conf file, but I did not need to do this since the line was already unity-greeter

(It's tricky for me to copy any output and paste it here as long as I have this problem, since I can't get to the desktop etc.)

After trying all this, I chose to just reinstall Ubuntu (11.10). After doing that the problem was gone! But as soon as I upgraded to 12.04 and rebooted I got the error message again 🙁

Then tried removing the file /etc/X11/xorg.config.failsafe and restarted lightdm GUI server as in this answer. This did not help either.

I also tried running startx and got:

kb@kb-HP-Compaq-4000-Pro-SFF-PC:~$ startx
X.Org X Server 1.11.3 Release Date: 2011-12-16 X Protocol Version 11,
Revision 0 Build Operating System: Linux 2.6.42-37-generic i686 Ubuntu
Current Operating System: Linux kb-HP-Compaq-4000-Pro-SFF-PC
3.2.0-41-generic-pae #66-Ubuntu SMP Thu Apr 25 03:50:20 UTC 2013 i686 Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.2.0-41-generic-pae
root=UUID=f5d21c1a-a302-4688-948b-470818bfb967 ro quiet splash
vt.handoff=7 Build Date: 11 April 2013  01:04:30PM xorg-server
2:1.11.4-0ubuntu10.13 (For technical support please see
http://www.ubuntu.com/support) Current version of pixman: 0.24.4
      Before reporting problems, check http://wiki.x.org
      to make sure that you have the latest version. Markers: (--) probed, (**) from config file, (==) default setting,
         (++) from command line, (!!) notice, (II) informational,
         (WW) warning, (EE) error, (NI) not implemented, (??) unknown. (==) Log file: "/var/log/Xorg.0.log", Time: Thu May  9 22:35:42 2013
(==) Using system config directory "/usr/share/X11/xorg.conf.d"

 Fatal server error: no screens found

 Please consult the The X.Org Foundation support
          at http://wiki.x.org  for help. Please also check the log file at "/var/log/Xorg.0.log" for additional information.

   ddxSigGiveUp: Closing log Server terminated with error (1). Closing
 log file. xinit: giving up xinit: unable to connect to X server: No
 such file or directory xinit: server error

I hope some of this info helps.