If you want Windows 10 and you are going to do a fresh install, just go download it from Microsoft's site, use their media creation tool to make a flash drive, and try installing it. It's possible they will let you have it for free. I heard rumors of this repeatedly so I tried it and it worked.
I had an old laptop where the hinge busted due to crappy design, so I got a different laptop, and used the broken one propped up on my desk to watch YouTube and stuff, but then later the hard drive died good. Didn't have a spare drive and didn't want to spend money on one for an old laptop so it sat for like a year until I ended up with a spare drive. Fixed the hinge with a lot of epoxy and superglue, wiped the spare HD that was from another system, installed it blank, and installed Win 10, and it just came up licensed to me.
Not sure why MS is still letting some people have Win10 free, but I'm not going to complain. The only thing I can think is that I had Win 8.1 on that system before it died and had all my systems linked to my Microsoft account, so maybe the system let me have it free because they knew I had the system when the Win10 upgrade was free? Don't know, but again, I'm not going to complain.
Worst case is that it will come up as unactivated and you'll have to decide if you want to install Linux or buy one of those $15 Chinese activation codes.