Windows Operating System automatically scans to determine whether your computer is running a real or counterfeit version of Windows. Sometimes, due to user error or virus activities, the Windows license key can change, causing your computer limited access to the operating-system features. Your computer will alert you in a number of ways if your Windows licensing key is not genuine. You can also use the command prompt to detect if the copy is genuine.
Click the "Start" button on your computer's desktop to launch the Start menu.
Type "cmd" in the textbox located in the Start menu and press the Enter key on your keyboard. This will launch the command-prompt window.
Type "slmgr.vbs /dlv" in the command-prompt window and press the Enter key on your keyboard. If you have a genuine copy of Windows, the software licensing status will appear in a new window. If you do not have a genuine copy of Windows, you will get an "Access denied" error instead.
Right click "Computer" from the Start menu and choose "Properties" from the menu.
Scroll down to the bottom of the "System" window and click "Change Product Key."
Follow the instructions to reenter your product key or enter a new genuine product key to fix authenticating problems.