I had a buddy who sold me his old gaming PC a few months ago, and I'm working on trying to get it up to speed. It's running Windows 10 Pro, but apparently it's not activated, so I'm dealing with the constant "Activate Windows" watermark. My hopes are that I can just buy a product key online without having to spend a whopping 200 dollars as advertised in the native store to have a genuine copy of windows running on my system.

So, to that end, I'm coming to ask for help from you guys. Anybody know of a good place to shop for Win 10 Pro product keys? I've found a few sites that offer the key for dirt cheap, but I'm worried that I'm gonna get scammed; I really don't have any experience dealing with this kind of stuff. Any PC I used in the past already had Windows installed so I never had to worry about it.

Oh, and fwiw, when I go to settings > activation, I see red text at the top that is telling me "We cant activate windows on this device as the previous version of windows was not activate prior to upgrading to windows 10. Go to the store to buy genuine Windows. Error Code: 0x803F7001" is that going to be a problem?