Format pc HD to MAC

hi, i have a MacBook with pc HD in it. Mac HD crashed so I replaced with pc hd from hp pavillion. That hd got Windows 7 on it and everytime I start up mcb is working like on pc. I don't want this. I tried use cd with Mac OS X but that don't work. I want Mac OS X back just like I never got HD crashed. Please help. I'm trying find some help for over week and still nothing.

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