Windows 10 TH1 is upgrade only and its digital deployment is thus fundamentally flawed creating Microsoft Product Activation issues such as those you are experiencing. Windows 10 TH2 will accept your Windows 7 OEM product key allowing for direct clean installation. Windows 10 TH2 is out on the Insider Preview and you can install it following my instructions here: [URL] It should be out on the maintrack soon.
 I bought a refurb system directly from Dell.  I've had issues with the system, but long story short, it was shipped with no OS loaded.  I was sent a disk with the appropriate OS - the system was advertised as coming with Win 7.  As soon as I got Win 7 loaded, I performed my free upgrade to Win 10. However, I cant get the license activated.  I get this error: Error Code: 0xC004C003Error Description:  The activation server determined the specified product key has been blocked  I'm not an expert, but it sure seems like I didn't get a legitimate copy of Windows...  Can someone please advise?  I'm getting a bit upset and do not feel I'm getting what I paid for... and really upset if a company like Dell cannot provide me with a legitimate product key.   
Not Provided a Valid Win 7 License?