I am sorry to have to ask this question, but I do not have the points to just comment on some of the similar questions:
Also, those might be outdated because Moab commented that with W10 build 1511, things might have changed a bit
Starting with W10 build 1511, you can use the W7 or W8 key on a clean install.
So, I have a Windows 8 Pro install DVD with a valid key and am trying to use that key on a new Windows 10 installation.
I used the Windows 10 Media Creation to create a bootable Windows 10 (I was not given an option for Windows 10 Pro) USB and I used that to install fresh Windows 10.
The windows installation let me use my Windows 8 Pro key when I was first prompted at the install, but after the install was done and I tried to activate the new Windows 10 installation I was told that the key is not working...
Can I skip upgrading Windows 8 Pro to Windows 10 and just install Windows 10 and use the key I have from my Windows 8 Pro?
After an update now I am getting this message:
This product key is already being used on another PC. Error code: 0x803FA071