W8 pre-installed is often OEM so the license dies (or stays) with the motherboard.
So yes to the question.
im building basically a new computer only keeping cpu ram and hard drive.
when i bought the computer im currently using it came with windows 8 pre installed to the mother board, but when windows 10 came out i upgraded, in new computer im building i want to put my OS on an ssd. am i able to move my OS to the ssd or do i need to buy another windows OS key?