Because the PC was bought with Windows 11 Pro preinstalled and only the hard drive was replaced, the license is most likely either:

1. An OEM key embedded in the device firmware (BIOS/UEFI), or
2. A digital license tied to a Microsoft account.

Use these options in order:

1. Let Windows auto-activate from firmware (OEM key)
   • Install Windows 11 Pro on the new drive.
   • Connect to the internet.
   • Go to Settings > System > Activation and check if it shows as activated.
     For many branded devices, the product key is stored in the BIOS/UEFI and Windows reads it automatically during installation, so no manual key entry is needed.
2. Check for a digital license / Microsoft account
   • If the PC was ever signed in with a Microsoft account, and the license was linked, activation may complete automatically once signed in with the same account.
   • Digital licenses are associated with the hardware and Microsoft account and do not require a visible product key.
3. Retrieve the OEM key from firmware (if Windows is running)
   If Windows is installed but not activated and the device is an OEM system (common with Amazon prebuilt PCs), the OEM key may be embedded in firmware. From an elevated Command Prompt, the OEM key can be read (as shown in the ROG example in the context) and then entered under Settings > System > Activation > Change product key.
4. Check purchase documentation
   • If the PC came with a separate Certificate of Authenticity (COA) label, card, or documentation in the box, the product key may be printed there.
   • If Windows 11 Pro was supplied as a separate digital license or upgrade, the key may be in the confirmation email or order details from the seller or from the Microsoft Store order history if purchased directly from Microsoft.
5. If no key or digital license can be found
   • For a new/refurbished device running Windows 11, activation normally uses a product key that is either preinstalled, on the packaging, or on a COA. If none of these are available and the firmware does not contain a key, contact the Amazon seller or device manufacturer and request the Windows 11 Pro key that should have been supplied with the PC.
   • If they cannot provide a valid key and the device cannot auto-activate, a new Windows 11 license can be purchased: go to Settings > System > Activation > Go to Store to buy a digital license.

If activation errors appear during these steps, use Settings > System > Activation > Troubleshoot and follow the guidance in the activation error help article referenced below.

References:

• Find your Windows product key
• Activate Windows
• Get help with Windows activation errors
• I cannot find my product key even though I purchased Windows - Microsoft Q&A
• How do I get my 2 year old ROG Zephyrus laptop Win 11 pro to stop showing "Activate Windows" - Microsoft Q&A