Windows Activation Error

0xC004C003: Product key blocked

0xC004C003 means Microsoft's activation server considers the product key you entered blocked or invalid. The most common causes are the key being active on another device, an edition mismatch (for example a Pro key on a Home installation) and revoked keys. In most cases verifying the edition and retrying resolves it.

Most common causes

• The key is currently activated on another computer
• The installed Windows edition does not match the key's edition (Home ↔ Pro)
• The key has been revoked by Microsoft or was counterfeit
• The activation server returned a temporary error under load

Step-by-step fix

1. Verify the installed edition: type "winver" into the Start menu and check whether it says Home or Pro; it must match your key's edition.
2. Wait a few minutes and retry — temporary server errors clear on their own.
3. Re-enter the key under Settings → System → Activation → "Change product key" (try typing it manually instead of pasting).
4. Run the "Troubleshoot" tool under Settings → System → Activation.
5. Press Windows + R → "slui 4" to open phone activation, pick your country and follow the automated line.
6. If the error persists, send the error code to the seller you bought the key from — invoiced sellers replace non-working keys.

Frequently Asked Questions

Other activation errors

• 0xC004C008Key usage limit exceeded
• 0xC004F050Invalid product key (edition mismatch)
• 0xC004F074KMS server could not be reached
• 0x8007007BSyntax/DNS error (KMS lookup)