why is my ATI graphics driver not working?

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http://askubuntu.com – i just installed ubuntu day ago and im total newb in this system. after installation and ubuntu update i found out in "System Info-"Graphics": Driver-Unknown, Expirience-Standard after that i found "Aditional Drivers" utility in "System Settings" and i found there 2 proprietary drivers: ATI/AMD proprietary FGLRX graphics driver (post-release updates) ATI/AMD proprietary FGLRX graphics driver when i activate first, it shows me error and it wont install. when i activate second, installs fine and asks for restart and after i restart graphics are slow and choppy, and youtube vids are slow (HowTos)