Millions of PC users around the world have used the free upgrade offer from Microsoft to upgrade their computers to the Windows 10 operating system. As you likely know, the Windows 10 upgrade is absolutely free for existing Windows 7 and Windows 8.1 users. Once you upgrade your Windows 7 or Windows 8.1 installation to Windows 10, your copy of Windows 10 is automatically activated. But it looks like many users are unable to activate their copy of Windows 10 and getting errors while trying to activate Windows 10. When you try to activate your copy of Windows 10, you might get “We couldn’t activate Windows. We can’t activate with this product key. Go go Settings for more information” error. To know the exact reason why your Windows 10 copy is not activated, please open the Settings app, click Update & Security, click Activation and then click Error details to view the error code and description. Once you have the error code, check the following error messages to know whey your copy of Windows 10 was not activated. Reasons why Windows 10 is not activated Following are the common Windows 10 activation errors and their meanings: The activation server determined the specified product key has been blocked (0xC004C003) This error appears if you have used a generic key or Windows 10 Preview key during the clean install of Windows 10. The error might also appear if you are using a key that has been blocked for some reason or if you had clicked the Skip button when you were asked to enter a valid product key while installing Windows 10. Genuine validation detected tampered Windows binaries. (Error code: 0xC004C4AE) The error mentioned above appears if you had installed a language pack in Windows 7 or Windows 8.1 using a third-party application. As you likely know, some editions of Windows 7, for instance, Windows 7 Home Premium edition doesn’t support adding a language pack. Still, there are many unofficial tools out there to help you install language packs in Windows 7 Home Basic and Premium editions. If you used a third-party tool to install a language pack, you might get this error. To fix the error, you need to go back to your Windows 7 or Windows 8.1 installation, and then remove the illegally added language pack. The software licensing service determined that this specified product key can only be used for upgrading, not for clean installations. (Error code: 0xC004F061 This error occurs if Windows 7 or Windows 8.1 was not installed on your PC before you tried using the product key to upgrade to Windows 10. As you likely know, in order to get the free upgrade, one must be running an activated copy of Windows 7 or Windows 8.1 Update. This product key didn’t work. (Error code: 0xC004C003) This product key didn’t work error might appear if you’re using an invalid product key to activate Windows 10. Please make sure that you haven’t typed a wrong product key. The activation server reported that the product key has exceeded its unlock limit. (Error code: 0xC004C020) This error usually appears if the product key is already used on another PC to activate Windows 10, or if the product key is being used on more PCs, then the software agreement allows. A networking problem has occurred while activating your copy of Windows. (Error code: 0xC004FC03) As the error description suggests, this appears if your PC is not connected to the internet. The error might also occur if the Firewall is preventing Windows from completing the activation. This error can be resolved by connecting your PC to the internet or temporarily disabling the Firewall software. The other solution is to activate Windows 10 by phone. A security error occurred. (Error code: 0x80072F8F) This error appears if Windows 10 is unable to connect to the activation servers or if the date and time on your PC are incorrect. Make sure that the date and time are correct and then try activating Windows 10 again. If you are not sure how to resolve the activation error, you can chat with Microsoft support or schedule a call back from Microsoft support.