It is booting without any problem, it didn't even ask me for username/password but after login, I can only see blank scree with right click my only option. Someone suggested that I should delete /etc/x11/xorg.conf file so I did that but without any luck. Can someone please help me?
First of all, do not randomly delete files, move them instead. My best advice at the moment is to boot a live CD, rename your home directory and create a new home directory. This way you can start clean, with the default GUI. If this is working then it's an issue with your personal settings and you don't have to touch system files.
You say 'your' GUI is broken after the upgrade, unfortunately we don't know what you mean by that. Which version were you using before? Which flavor of Ubuntu (Kubuntu, Xubuntu, Lubuntu...)? What changes have you made to the default GUI? Did you install additional packages and perhaps PPAs for achieving that? Are those packages still installed or have those packages been reinstalled after the upgrade? The upgrade script disables PPAs as far as I know.