Somebody please help me, desperate... please

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http://askubuntu.com – I followed a friend's advice and am using Ubuntu, and was enjoying it. I began to get system errors, tried to fix to no avail. It won't let me download anything to Ubuntu, saying unauthorized or untrusted software, or something. NOW MY CD DRIVE doesn't work! So I can't boot dban or anything via cd. Finally I bought a usb stick but it won't boot dban or anything. I'm about to just smash this with a hammer. Help me start over. (HowTos)