| Error code | Usual meaning | What to do |
|---|---|---|
0xC004F050 | The key isn't valid for this installation. | Check the edition matches the key and re-enter it carefully. Key not working. |
0x803F7001 | No valid product key or digital license was found for this PC. | Enter a product key for your edition in Settings › System › Activation. |
0xC004F213 | No product key was found on the device, often after replacing the motherboard. | Use the Activation troubleshooter or re-enter your retail key. Hardware changes. |
0xC004F211 | Windows detected that the hardware changed. | Run the troubleshooter and choose "I changed hardware on this device recently". |
0xC004C003 | The activation server rejected the key. | Confirm the key was entered correctly. If it was, contact the seller with the code. |
0xC004C008 | The key has already been used on the number of PCs its license allows. | Deactivate the old PC, then try the Activation troubleshooter or, on supported builds, phone activation (slui 4); otherwise contact the seller. |
0xC004F074 | Windows is trying to reach a KMS (volume) server, typically on a PC previously in a company. | Install your retail or OEM key with slmgr /ipk, then run slmgr /ato. |
0x8007007B | A volume license key is installed and no KMS server is available. | Replace it with your own key using Change product key. |
0x80072F8F | Secure connection failed, often because the date or time is wrong. | Set time automatically, sync, and try again. |
0x87E10BC6 | The activation service couldn't be reached. | Check your connection and try again later; the issue is usually temporary. |
Using the Activation troubleshooter
When Windows isn't activated, Settings › System › Activation shows a Troubleshoot option. You need to be signed in as an administrator. The troubleshooter can detect edition mismatches and, after a hardware change, reactivate a digital license linked to your Microsoft account.
Useful commands
Run these in Terminal (Admin):
slmgr /dlvshows detailed license information, including the license channel (Retail, OEM or Volume).slmgr /ipk YOUR-KEYinstalls a product key.slmgr /atoattempts online activation and reports the error code if it fails.slui 4starts phone activation on supported builds. On newer builds where that option is unavailable, use the Windows Activation troubleshooter or Microsoft's activation support options.
Error not listed?
Start with the general checklist. If you bought your key online, send the seller's support team the code, your edition and your order number.