The Windows activation error code 0xC004C008 occurs when the activation server identifies your product key as already used on another device or when the key has reached its activation limit. This issue commonly arises after hardware upgrades, such as changing your motherboard, or when reinstalling Windows on a new device. Fortunately, there are several straightforward methods to resolve this issue and successfully activate your Windows.

Method 1: Activate Windows via Phone Activation

The most effective and widely recommended solution for the 0xC004C008 error is activating Windows through phone activation. Follow these detailed steps:

Step 1: Press the Windows key + R to open the Run dialog box. Type SLUI 4 and press Enter. This action opens the Phone Activation window.

Step 2: Choose your country or region from the drop-down menu and click "Next". You will see a phone number to call, specific to your region.

Step 3: Dial the provided activation number. You will be asked to enter your Installation ID via your phone keypad. Follow the automated prompts carefully.

Step 4: When asked how many devices your product key has been installed on, select "1". Choosing any other option may prevent successful activation.

Step 5: After verification, the automated system will provide a confirmation ID. Write this down carefully.

Step 6: Enter the confirmation ID into the provided fields on your screen and click "Activate". Your Windows should now activate successfully.

Method 2: Run the Windows Activation Troubleshooter

If phone activation isn't an option, the built-in Windows Activation Troubleshooter can help resolve licensing issues automatically. Here's how to use it:

Step 1: Press Windows key + I to open Settings. Navigate to "Update & Security" and select "Activation" from the left pane.

Step 2: In the Activation section, click on "Troubleshoot". The troubleshooter will begin diagnosing activation problems.

Step 3: If the troubleshooter identifies an issue, click "Apply this fix" and follow any on-screen instructions provided.

Step 4: Restart your computer after the troubleshooter completes its process. Check if Windows is activated successfully.

Method 3: Contact Microsoft Customer Support

If neither of the above methods resolves the issue, contacting Microsoft Customer Support directly is your next best step.

Step 1: Visit the official Microsoft support page here and initiate a live chat session or request a callback from a Microsoft representative.

Step 2: Explain your issue clearly, mentioning the error code 0xC004C008 and the circumstances under which it appeared (e.g., hardware upgrade, motherboard replacement).

Step 3: Provide the representative with your product key and any relevant details. They will assist you in resolving the activation issue remotely.

After following these methods, your Windows activation error 0xC004C008 should be resolved, allowing your system to run smoothly again.