Windows 10 Setup has failed to validate the product key

What edition of Windows will I get as part of this free upgrade?

Some editions are excluded: Windows 7 Enterprise, Windows 8/8.1 Enterprise, and Windows RT/RT 8.1. Active Software Assurance customers in volume licensing have the benefit to upgrade to Windows 10 enterprise offerings outside of this offer.

What about Windows RT?

If you’re running Windows RT, your device won’t upgrade to Windows 10, but we will have an update for you around the time of Windows 10 release.

Can Enterprise customers get the free Windows 10 upgrade?

Enterprise customers with active Software Assurance subscription in volume licensing have the benefit to upgrade to Windows 10 enterprise offerings outside of this offer.

More in Specifications.

These are for a pre-released version of Windows 10 and are subject to change.

I always use Nirsoft's Produkey for this. Most reliable toolset for all sorts of such simple things. Highly recommended.

ProduKey is a small utility that displays the ProductID and the CD-Key of Microsoft Office (Microsoft Office 2003, Microsoft Office 2007), Windows (Including Windows 7 and Windows Vista), Exchange Server, and SQL Server installed on your computer. You can view this information for your current running operating system, or for another operating system/computer - by using command-line options. This utility can be useful if you lost the product key of your Windows/Office, and you want to reinstall it on your computer.

Supported Products List

Microsoft Windows 98/ME Microsoft Windows 2000 Microsoft Windows NT Microsoft Windows XP Microsoft Windows Vista Microsoft Windows Server 2003 Microsoft - Windows 7 (Doesn't work with Microsoft Volume Licensing) - Microsoft Windows 8 (Doesn't work with Microsoft Volume Licensing)

This is the answer you needed. For things beyond the original question, the following may help in addition to Fleet Commands's answer.

Regarding upgrading to or installing Windows 10, you might be better served with Fleet Command's answer and digging into this in more detail on Windows 10 upgrade specific forums like MSFN and MyDigitalLife.

Without assuming what licenses you are using legit or not, and I am not sure SuperUser will allow/ or support your licensing upgrade path, if it is not kosher in the eyes of Microsoft. I've found every forum has their own rules regarding 'licensing' tips/ hacks to prevent conflicts with Microsoft Corp.

The answer can vary a lot depending on the original license and version you have and the Windows 10 you are upgrading to and also variation between how OEM licenses from Windows 7 will give you Windows 10 but it may be for that machine only.