Ubuntu :: Login Window Does Not Appear After Boot Up

My laptop did a "shutdown" (not reboot) automatically over night when I was downloading few things. When I tried to boot it up, it boots up & it never displays the window which asks for password. I have tired to reboot it several times since then it still stays at the same place. Since it is not displaying username & password window & I am not able to login through gdm. Interesting thing is the normal sound which comes when the login window is display is heard but the window is not seen. However when I press ctrl+alt+f5 I am able to login there which is only text based login.

I tried several things to get out of issue like
1) In the console run
ps -eaf | grep -i gdm
I see that the login process is running but is not displaying the window.

2) sudo dpkg-reconfigure xserver-xorg ( it didnt ask me anything about the driver or anything like that & just returned with out any error message )
$? of the above command was 0.
==> reboot after this & still the login window would not come.

3) After login at the console ( ctrl_alt+f5 )
sudo service gdm stop ==> no error prints
sudo service sdm start ==> no error prints
==> no login window

4) apt-get remove ubuntu-desktop
apt-get install ubuntu-desktop
==> no login window

5) export DISPLAY=:0.0
sudo -u gdm gnome-control-center 2>gdm.txt ( this the attached error messages)
ctrl+alt+f7
==> no login window

I would hate to reinstall ubuntu again cause of the amount of software + data + personalization.