How to get my activation/product key?

I just bought a Lenovo all in one computer from best buy earlier today. Ive never had a problem with getting computers from them until today. For whatever reason, my Windows 8.1 is not activated. I thought it was automatically supposed to be activated. I dont know where or how to find the product key. Its nowhere on the computer itself and its not on the box either. How can I find this info so I can activate windows and upgrade to windows 10?

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