Old ATI card and xorg/lightdm

try blacklisting the driver

If you have an xorg.conf file (probably you have one), rename it to xorg.conf.old and try to start without xorg.conf at all.

Then post again your xorg.conf file. Full results it would be better.

    sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.old

Regards
 NikTh

I restarted without xorg.conf and it again reached a blinking black screen. No new xorg.conf is generated. Here is the only xorg.conf that will work at all.

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

Section "Monitor"
 Identifier "Configured Monitor"
EndSection

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

This is the full contents of x-0.log from /var/log/lightdm, showing how X crashes when loading the GLX extension.

X.Org X Server 1.13.3
Release Date: 2013-03-07
X Protocol Version 11, Revision 0
Build Operating System: Linux 3.2.0-37-generic i686 Ubuntu
Current Operating System: Linux b-PCG-FX401-GB 3.8.0-19-generic #29-Ubuntu SMP Wed Apr 17 18:19:42 UTC 2013 i686
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-19-generic root=UUID=d02c1a8f-5698-4a8c-8eac-851ce3f965df ro quiet splash vt.handoff=7
Build Date: 17 April 2013 10:42:56PM
xorg-server 2:1.13.3-0ubuntu6 (For technical support please see http://www.ubuntu.com/support)
Current version of pixman: 0.28.2
 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: Mon May 27 12:29:37 2013
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
Initializing built-in extension Generic Event Extension
Initializing built-in extension SHAPE
Initializing built-in extension MIT-SHM
Initializing built-in extension XInputExtension
Initializing built-in extension XTEST
Initializing built-in extension BIG-REQUESTS
Initializing built-in extension SYNC
Initializing built-in extension XKEYBOARD
Initializing built-in extension XC-MISC
Initializing built-in extension SECURITY
Initializing built-in extension XINERAMA
Initializing built-in extension XFIXES
Initializing built-in extension RENDER
Initializing built-in extension RANDR
Initializing built-in extension COMPOSITE
Initializing built-in extension DAMAGE
Initializing built-in extension MIT-SCREEN-SAVER
Initializing built-in extension DOUBLE-BUFFER
Initializing built-in extension RECORD
Initializing built-in extension DPMS
Initializing built-in extension X-Resource
Initializing built-in extension XVideo
Initializing built-in extension XVideo-MotionCompensation
Initializing built-in extension SELinux
Initializing built-in extension XFree86-VidModeExtension
Initializing built-in extension XFree86-DGA
Initializing built-in extension XFree86-DRI
Initializing built-in extension DRI2
Loading extension GLX
(EE)
(EE) Backtrace:
(EE) 0: /usr/bin/X (xorg_backtrace+0x49) [0xb76f9f49]
(EE) 1: /usr/bin/X (0xb754c000+0x1b1e86) [0xb76fde86]
(EE) 2: (vdso) (__kernel_rt_sigreturn+0x0) [0xb752940c]
(EE) 3: /lib/i386-linux-gnu/libc.so.6 (0xb7131000+0x7fed6) [0xb71b0ed6]
(EE) 4: ?? [0xb7b23788]
(EE)
(EE) Segmentation fault at address 0x0

Fatal server error:
Caught signal 11 (Segmentation fault). Server aborting

(EE)
Please consult the The X.Org Foundation support
  at http://wiki.x.org
 for help.
(EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
(EE)
Server terminated with error (1). Closing log file.

You may need an xorg.conf file to define the display better