Step 1:
Open the official website

Step 2:
Sign in to your personal Microsoft account

Step 3:
Enter the 25-digit product key

Step 4:

Select the language and number of products in "Other Installation Options" according to your personal needs.

Step 5:

Select Phone Activation.

Enter the numbers from your activation window on the phone's keypad when prompted by the phone's voice.

Step 6:

The phone voice will give you verification IDs to complete the activation. Enter this in step 3.

Step 7:

When the phone voice asks "How many copies do you have installed?", type "1" on the phone's keypad.

IF THE PHONE ACTIVATION FAILED: In this case you will be transferred to a Microsoft agent. Microsoft is unable to provide support for product keys not sold directly by them. Contact us directly and we will help you.