When using the Windows 8.1 operating system for the first time, you need to activate it within a certain period of time in order to continue using it. This is very easy to do with instructions and an activation key already included in the installer package. But if you somehow lost your activation key, there are additional ways to activate this system.
Steps
Part 1 of 2: Recovering a Lost Key

Step 1. Download the key recovery program
The Windows activation key is stored in the registry and can be retrieved from there using a special program. The most popular programs are ProductKey and Key Finder.
These are free programs that can be downloaded from their developers' websites. There are also paid versions of these programs, but the free version will be enough to extract the Windows key

Step 2. Run the program to recover the key
As a rule, you do not need to install such a program. Just run it and a list of available keys will be displayed. Find the Windows entry and its corresponding key.

Step 3. Write down or copy the key
The key will be labeled as "Product Key" or "CD Key". The Windows activation key consists of 25 characters, divided into five groups (five characters per group).
Part 2 of 2: Activating Windows 8.1

Step 1. Open the activation window
To do this, press ⊞ Win + R and type slui 3. Press ↵ Enter to open the window.

Step 2. Enter the activation key
Enter the key that is listed on the computer case, or on the Windows installation disc, or that you extracted from the registry. You do not need to enter “-” (dash) characters as they are added automatically. After entering the key, Windows will try to automatically activate.

Step 3. Use the command line
If the above steps did not work, you can try entering the key in the command line. Press ⊞ Win + X and select Command Prompt (Admin).
- Type slmgr.vbs / ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX and press ↵ Enter; substitute the activation key instead of XXXXX. Be sure to enter the “-” (dash) characters. A window with the message "Key XXXXX has been successfully installed" should open.
- Type slmgr.vbs / ato and press ↵ Enter. A window with the message "Windows Activation (R) System Version" should open. If the activation was successful, a window with the message "Product activated successfully" will open.

Step 4. If you still cannot activate the system, contact Microsoft, namely the automated Windows activation service
To find the number in your area, press ⊞ Win + R and enter slui 4. A window with contact information and installation ID will open.
Make a note of the installation ID as you will need to enter it over the phone. This is a long but necessary process of recognizing your computer
Advice
- The product key is already included in the Windows 8.1 package. If you have such a key, you do not need to install it using the command line.
- The product key can only be used on a limited number of computers. If you reach the maximum number of computers, the key will become invalid.
- This article was written for educational purposes only. Always purchase and activate Genuine Windows 8.1 to avoid software problems.
- With the release of a new version of Windows, Microsoft has made changes to how it distributes its product key. Currently, the product key for Windows 8 is embedded in the BIOS of the computer, rather than on a sticker that is located on the computer. This affected many users: some of whom were satisfied with this innovation, and others not very much.
- Be careful when performing this step on the Xbox. They can lead to complete damage to the device.