[ubuntu] Desktop Nonresponsive -- HELP!

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http://ubuntuforums.org – System is ubuntu 12.10 with optional Mate desktop. I changed the command in "Users & Groups" (under Administration) by simply adding "gksudo" at the beginning. I thought this way I won't have to login every time. I've done this for Synaptic, Software-Center and a couple of others and it works fine. Running the command "Users and Groups" with gksudo brought up an undresponsive window,I couldn't get rid of it so I rebooted. Now, system boots up fine, but it's non-responsive. Main menu is frozen. Help, how do I get out of this?? (Hardware)