Ubuntu 12.04 always giving error whenever installation required [closed]

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http://stackoverflow.com – Whenever I run sudo apt-get install AnySoftwareOrPackageName It shows Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to locate package Please help me solving this problem asap ... I think this is happening due to the changes I did in Ubuntu Software centre's software resources . The /etc/apt/sources.list file is as follows : deb cdrom:[Ubuntu 12.04 LTS _Precise Pangolin_ - Release i386 (20120423)]/ precise main restricted deb http://mirror1.ku.ac.th/ubuntu/ precise universe deb http://mirror1.ku.ac.th/ubuntu/ precise mai (HowTos)