Finally after lot of struggling, I was able to resolve this issue. And I happily writing this answer from the same Ubuntu which I lost for few hours.
If the Ubuntu is not booting up, then when the blank screen appears press
Ctrl + Alt + (F1 to F6, anything) or goto recover mode to check from the command line.
Then, I checked following file:
sudo vi /var/log/Xorg.0.log
It will give you the information, where exactly you are failing. For example, it was failing for me in one of the files which I wrongly edited. See the bold text below.
X.Org X Server 1.10.4
Release Date: 2011-08-19
[ 16.685] X Protocol Version 11, Revision 0
[ 16.685] Build Operating System: Linux 2.6.24-29-server i686 Ubuntu
[ 16.685] Current Operating System: Linux Ubuntu11.10 3.0.0-13-generic #22-Ubuntu SMP Wed Nov 2 13:25:36 UTC 2011 i686
[ 16.685] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.0.0-13-generic root=UUID=0e1d28e3-b3cc-4022-81c6-4f4d24ac6f63 ro quiet splash vt.handoff=7
[ 16.685] Build Date: 19 October 2011 05:09:41AM
[ 16.685] xorg-server 2:1.10.4-1ubuntu4.2 (For technical support please see http://www.ubuntu.com/support)
[ 16.685] Current version of pixman: 0.22.2
[ 16.685] Before reporting problems, check http://wiki.x.org
to make sure that you have the latest version.
[ 16.685] Markers: (--) probed, (**) from config file, (==) default setting,
(++) from command line, (!!) notice, (II) informational,
(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
[ 16.685] (==) Log file: "/var/log/Xorg.0.log", Time: Sat Nov 26 22:59:34 2011
[ 16.865] (==) Using system config directory "/usr/share/X11/xorg.conf.d"
[ 17.051] Parse error on line 14 of section InputClass in file
"ppa:sergio91pt/synaptics+clickpads" is not a valid keyword in this section. [ 17.051] (EE) Problem parsing the config file [
17.051] (EE) Error parsing the config file [ 17.051] Fatal server error: [ 17.051] no screens found [ 17.051] Please consult the
The X.Org Foundation support
I simply removed that line and rebooted. It again appeared with blank screen, I just tried randomly other
tty section (e.g.
tty2), by pressing
Ctrl + Alt + F2 and I to my pleasant surprise I saw the graphical login screen!!!
I just checked if everything is intact. Also, due to upgrade, I see small changes in usability, but rest is fine otherwise. This is my first successful login after that disaster and I hope that it will continue without any problem in future.
Lesson, I learned were, to fix a small problem don't do unnecessary upgrade/updates and screw your time and energy. Thanks.