ProductKey

Follow these steps to try reactivating Windows on the same device after formatting:

1. Check the exact activation error code
   Go to Start > Settings >
   • Windows 11: System > Activation
   • Windows 10: Update & Security > Activation
     Note the error code shown (for example: 0xC004C003, 0xC004F034, 0x803F7001, 0x800704CF, etc.). The resolution depends on this code.
2. If the key is reported as invalid (e.g. 0xC004C003 or 0xC004F034)
   These errors indicate the product key is not valid for the installed edition or has been used in a way that is not allowed.
   • Make sure the installed edition (Home/Pro, 10/11) matches the license that came with the PC. If the wrong edition was installed, use the Activation Troubleshooter:
     • Windows 11: Start > Settings > System > Activation > Troubleshoot.
     • Windows 10: Start > Settings > Update & Security > Activation > Troubleshoot.
       If a valid digital license for a different edition is found, it will offer to switch to the correct edition.
   • If the key still fails and the device is new or came with Windows preinstalled, contact the device manufacturer or the reseller, as recommended for error 0xC004C003.
3. If Windows reports no valid license found (e.g. 0x800704CF or 0x803F7001)
   These errors mean Windows cannot find a valid license for the current installation.
   • Enter the 25‑character product key again:
     • Windows 11: Start > Settings > System > Activation > Change product key and enter the key.
     • Windows 10: Start > Settings > Update & Security > Activation > Change product key and enter the key.
   • If activation still fails, run the Activation Troubleshooter from the same page. If you see an option like I changed hardware on this device recently or reactivate after a hardware change, follow that path to re-associate the digital license with the device.
4. If you recently changed hardware (motherboard, etc.)
   A preinstalled (OEM) license is normally tied to the original hardware. After major hardware changes, Windows may not find a matching license and can show errors like 0xC004F211 or 0xC004F213.
   • Sign in with the same Microsoft account previously used on this device.
   • Go to Settings > System/Update & Security > Activation > Troubleshoot and follow the reactivate after a hardware change path if offered.
   • If the motherboard was replaced on an OEM device, a new license may be required.
5. If none of the above works
   • Confirm the product key from the original documentation (sticker/COA, packaging, or email).
   • If the key is genuine and still rejected, and the device came with Windows preinstalled, contact the device manufacturer.
   • If the key was purchased separately and is reported as invalid (for example 0xC004C003), contact the reseller.

For detailed behavior and additional troubleshooting per error code, use the Activation Troubleshooter and the guidance in the referenced articles below.

References:

• Get help with Windows activation errors
• I cannot find my product key even though I purchased Windows - Microsoft Q&A
• Unable to activate Windows after reinstall - Microsoft Q&A
• Unable to use troubleshooter for windows activation - Microsoft Q&A
• Reactivate Windows 11 - Microsoft Q&A
• Can't Activate Windows after MSFT Forced Upgrade to 11 - Microsoft Q&A