By Anthony 
When you have to reinstall Windows Server now you can only install a Evaluation version. Which is no problems, but what happens if the key you have doesn’t work right off the back? No problem 99% of the time this is due to the installed server being a Windows Server Evaluation Version. You have a purchased key for your Standard, Data center, what have you. So how do we reset this
Turns out Microsoft has a tool for this, and its pretty easy to make work.
You may download the Windows Server installation media from Microsoft using the following links:
Windows Server 2022 Eval
https://www.microsoft.com/en-us/evalcenter/download-windows-server-2022
Windows Server 2019 Eval
https://www.microsoft.com/en-us/evalcenter/download-windows-server-2019
Windows Server 2016 Eval
https://www.microsoft.com/en-us/evalcenter/download-windows-server-2016
Keep in mind that these will install as “Eval” versions. In order to activate using your product key, you need to convert it to Standard first. If your product key is for Windows Server Essentials, you still need to convert it to standard as the binaries for both versions are the same and only the licensing terms change.
Converting Eval Version to Standard for activation
After you installed the desired Windows Server version from the links above, boot to the desktop and launch an elevated command prompt. Then type in the following and hit enter (replace the XXXXX-XXXXX-XXXXX-XXXXX-XXXXX section with a product key from the list below):
dism /online /set-edition:serverstandard /productkey:XXXXX-XXXXX-XXXXX-XXXXX-XXXXX /accepteula- Windows Server 2016
CKYTP-RN8TV-XJF97-JCRFV-RGD96 - Windows Server 2019
KCNPH-BQTCW-CG2QQ-9FHM9-KQDD4 - Windows Server 2022
VDYBN-27WPP-V4HQT-9VMD4-VMK7H
This will convert your Eval installation to Standard. After restarting the system, you may use your actual product key to activate through the GUI. Do not use your product key in the command above as it will fail, this step is only for setting the OS to the default Microsoft key so that it prompts for the real one.