What key do I Use, I'm  using the windows 8.1 key that came with the computer and it won't take the key. It is a 2in1 Computer that is 2 months old. I downloaded the windows 10 from Microsoft to an installation USB drive. but it refuses any activation keys.

Hi roberttcz,

The Windows 8.1 product key cannot be used to activate the Windows 10 clean installation.

To upgrade to Windows 10, we could click the "Get Windows 10 app" from the taskbar. If you have`t got that app, we could check for updates manually for the machine to get the update "KB 3035583". This update is an app to get Windows 10. We may need to restart the machine to make the update take effect.
We could run "wusa /uninstall /KB:303583" to verify whether this kb has been installed.
Once this update has been installed, we will get an app on the right bottom. Then we can click this app and following the instructions to get Windows 10.

Best regards

Hi,

In addition, to use Media installation tool to install Windows 10, we have to choose Upgrade option and skip the enter product key step.

For clean installation, you have to buy the key from Microsoft store. we cannot activate Windows 10 by using Windows 8.1 key.

If your activation still fail, we may have to revert back to Windows 8.1 and make sure the activation status, then try to upgrade again.