Unfortunately, manually locating the Windows 8 product key in the registry isn't possible, so you'll need to use a program like this.
N'ụzọ dị mwute, iji aka na-achọpụta akara ngosi Windows 8 na ndekọ ahụ agaghị ekwe omume, yabụ ị ga-eji usoro ihe omume dị otú a.