Firstly, please make sure that you have installed the correct Windows version. Download links for the installation files are always available on the product page in the Activation Details tab.
Also, please keep in mind that since this is an OEM license this key cannot be used to upgrade or downgrade - you have to perform a clean installation.
If you have installed the correct Windows version and you are still unable to make use of your license (for example due to an error 0xC004C008), please use the automated phone system as in most cases this method solves the issue. In order to start the phone activation please type “SLUI 04” in the search box on the taskbar and press “Enter”. Then follow the instructions on the screen to activate Windows.
In case of any trouble with the activation, please remember that you can always contact Microsoft support via LiveChat for additional assistance with the process.
If they confirm that you are unable to activate your license due to an issue with the code, then please provide us with the following unedited screenshots:
1. with the confirmation from MS LiveChat Support that this particular key is indeed unusable;
2. with the entered key before the activation;
3. with the error message you received;
4. with the details of the current version of the system.
Please make sure that the screenshots are full and uncropped. Your whole screen should be visible in it, including the Windows taskbar with the time/date.