Hi, Steven Druckman
The registry backup may contain a generic installation key rather than the original transferable license key. Changing from MBR to GPT does not normally affect activation, but replacing the motherboard creates a new hardware identity.
Besides the solutions provided by the Q&A Assist, here are some suggestions you can try:
Press Windows key + R, enter slui 4, and press Enter. Select your country or region, then use the displayed Installation ID with the offline Product Activation Portal. Enter the Confirmation ID you receive to complete activation. Offline activation is specifically available when normal online activation does not complete.
Open Command Prompt as administrator and run:
slmgr /dlv
Check the Description and Product Key Channel. If it shows Retail, the license may be transferable. If it shows OEM_DM or OEM, it was likely supplied with the original motherboard and normally cannot be moved.
If the license was purchased separately, check the purchase email, retail package, or Microsoft account order history for the original key. Do not rely on a key recovered from the registry, since Windows may display a default key instead of the actual OEM key.
If no transferable retail license can be verified, purchasing a new license may be necessary.
Thank you for your patience in reading, I hope this information has been helpful to you.
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