Χάσατε ή ξεχάστε το κλειδί ενεργοποίησης των Windows που usesτε; Παρακάτω θα δούμε πως μπορείτε να ανακτήσετε το κλειδί προϊόντος από ένα εγκατεστημένο functional Windows 10, Windows 8 or Windows 7, with one command.
It is the simplest solution to find your product key from an operating system system Windows that is already installed on your computer without using any third-party software. 
You should open a command prompt window and run the following command.
To open a command prompt window search for "cmd" or "cmd.exe", and open the black icon that will appear first in search results.
Type the following command:
wmic path softwarelicensingservice get OA3xOriginalProductKey
It will show you the product key of your operating system.
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Update:
If the above command does not work on your system, open a notepad and copy and paste the following text:
Save it to your desktop with the extension .vbs. You can use a name you want, for example, iguru.vbs.
Below you can download it ready archive. Open the .zip and double-click the iguru.vbs file. It will tell you your OS key.
