[ubuntu] a peculiar situation without an admin user

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http://ubuntuforums.org – I am using ubuntu11.10 64 bit version . while checking the user account i have changed my admin user as an standard user. As aresult there is no more admin user. and here the problem begins . whereever authentication is needed it is asking for admin password . the former admin password is not working , as it has became a standard users password .I am unable to make that account an admin one as this also recquire an admin password. As a result i can not install any app from ubuntu software centre or even can not download security update. what should i do? please suggest me. (Hardware)