Installing genuine restore Windows 8.1 and genuine product key got you here in the first place. Starting with Windows 8.1, Dell OEM product keys are embedded on the motherboard.  No more product keys on COA sticker and no genuine OEM product key in Windows installation software, except digital retail product key (on sticker or email)  If your machine was shipped with Windows 8.1 license, Microsoft still allows upgrade to Windows 10/11.  So, directly installing Windows 10 and activate it with Windows 8 license is a better path to take.
I'm trying to restore a Dell 7910 back to factory after a hard disk failure and installed replacement. I'm following the process laid out here..... [URL] The Tag number for the machine is valid and gives me a download option of circa 580Mb, I then on a different machine (that's running Windows 11) unpack that zip file and follow the process to generate the USB stick for the T7910. However, when I use that USB stick on the 7910 and boot from it, after a few checks are undertaken a message comes up saying the key is either invalid or modified (I can't remember the exact wording) and to recheck and try again. I've now run the process three times and downloaded the appropriate files from Dell twice, all with the same result. The original installation on the 7910 was Windows 8.1 according to the Dell system info page for the tag number, although I don't know if there's a way to tell what version of windows is unpacked from the zip that's downloaded. Any ideas
T7910 Windows Restore - Invalid Key Error?