According to Dell's website the Windows licence is specifoc to each particular machine and its details are burned into the BIOS.
Is it possible that the original OS was Home edition (in which case the licence is not valid for Pro)?
Have you tried installing a Home edition?

The mechanics of Windows activation is well discussed so I won't breach that topic. To your last question, yes. Also, for home users it doesn't matter if it activates later as Home or Pro.

Has who tried home edition? I’m so confused. This seems like a response to someone else’s question.

Yes, Dell and many other manufacturers embed the Windows license key into the BIOS/UEFI firmware of the machine. This means that the license key is tied to the specific hardware and can be automatically detected and used during the Windows installation process.

Possible Issues with License Edition
Edition Mismatch: If the original OS was Windows Home edition and you are trying to install Windows Pro edition, the embedded key will not work. Windows will not activate if there is a mismatch between the installed edition and the edition of the embedded key.
Steps to Resolve the Issue
Determine the Original Edition:

You can check the edition of Windows that was originally installed on the machine using the BIOS key.
Use a tool like the Windows Product Key Viewer or check in the UEFI firmware settings.
Install the Matching Edition:

If the original OS was Windows Home edition, try installing the Home edition.
During the installation process, Windows should automatically detect the embedded key and activate the correct edition.
How to Install the Correct Edition
Create Installation Media for Windows Home:

Download the Windows Media Creation Tool from the Microsoft website.
Use the tool to create a bootable USB drive for Windows Home edition.
Installation Process:

Boot from the USB drive.
During the installation process, Windows will detect the embedded key and install the corresponding edition (Home).
If prompted to enter a product key, choose the option to skip or select "I don't have a product key."
Activation:

Once the installation is complete, Windows should automatically activate using the embedded key.
You can check the activation status by going to Settings > Update & Security > Activation.
If Pro Edition is Required
Upgrade from Home to Pro:
If you need Windows Pro, you can first install Windows Home using the embedded key.
Once Windows Home is installed and activated, you can purchase an upgrade to Windows Pro from the Microsoft Store or by entering a valid Pro product key.

commented: All very valuable information. +0

The above is all very valuable information. One aspect that wasn't mentioned for those of you who do hardware repairs, in the case where you must replace the motherboard you will no longer have a valid key unless you have written down or saved to backup the key for the damaged motherboard. In which case you will need to purchase another valid key. Interminable calls or chats to Dell or Microsoft, etc. to explain your unfortunate situation, will do you no good. It is prudent to keep a copy of any keys that you have for all computers. You can use Speccy or Belarc for a wealth of info regarding your machines.

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