Hi, If you haven't done anything yet about the reinstall of an OEM O/S, check with a program such as 'Speccy' by Piriform, in the 'Operating system section', what your product key actually is.
I have seen a Laptop bought from a well-known UK pc dealer, where the Product key on case sticker, was not the real (activated) one. So in that case I made a note of the key as given by 'Speccy', written down on paper, in case it was needed in the future. There are several other programs that will search the pc for the product key.
e.g. Magical jelly bean key finder. (Yes it's real.)