Activation error

0xC004C003

The activation server determined the specified product key is blocked

Microsoft's activation server has blocked the product key you entered. A key is blocked when it was already used (or attempted) on more devices than the license allows, or when it was never validly issued. You need a different, valid key to activate Windows.

Symptoms

Settings > System > Activation shows "Windows is not activated"
Error text: "The activation server determined the specified product key is blocked"
The Activation troubleshooter reports it can't activate this copy of Windows

Causes

The product key was used on (or attempted on) more devices than the Microsoft Software License Terms allow
The key was never validly issued — for example a counterfeit or mistyped key
A volume (MAK/KMS) key on the Microsoft side was blocked by the licensing activation center

How to fix it

Confirm which key is installed

Open an elevated Command Prompt and run slmgr.vbs /dli to see the license description and the last five characters of the installed product key. Compare those characters with the key you were sold.

Run the Activation troubleshooter

Go to Settings > System > Activation and select Troubleshoot. If your digital license is linked to your Microsoft account, signing in with that account can reactivate Windows automatically.

Re-enter a valid product key

In Settings > System > Activation, select Change product key and enter a valid 25-character key that matches the Windows edition installed on the device (for example Windows 11 Pro, not Home).

Contact whoever sold you the key

If the key was blocked on Microsoft's side, a legitimate seller can replace it. If you bought a device with Windows preinstalled and saw this on first boot, contact the device manufacturer.

Still need help?

If error 0xC004C003 keeps blocking activation after these steps, our support team can check your key and license channel directly.

Contact support

Genuine licenses

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Windows 11 Home

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