Windows vista product key not vissible on lap

Hello,
i bought hp pavillion dv4 1125nr 13 months before.yesterday i format the hard drive,my recovery drive also formatted.then i intall win 7 but now i want to install windows vista again,i have no recovery cds.now how can i get my geniun windows vista home premimum back?i also download windows vista from torrent site but needs PRODUCT KEY,which is NOT CLEARLY VISIBLE on lower side of laptop............please help............how can i get this key?