Unable to login for a user from GUI?

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http://askubuntu.com – I tried to install the graphic card drivers for my raedon hd 6400 series yesterday. Since the installation didn't went fine I had to remove the installed driver; and after since I rebooted I am not able to login (from GUI) for that user whereas I can login from command line. I created a different user for use; but the newly created user don't have the privileges of running the sudo with admin commands.like for software installation. I have followed various links for login loop but they are not helping. Please help. At this point I am not sure which logs should I paste here. (HowTos)