Lots of Windows 7 users have experienced the error message that "Windows 7 is not Genuine". This error message comes if you use pirated or OEM versions of Windows 7. If windows 7 is not genuine, even you can't change the background wallpaper or any other display related option on your PC.
1. Press Windows key + R
2. Now "run" box will appear , In the "run" box type CMD, Click on OK
Note:- Run CMD as Administrator Now command prompt will appear In command prompt type SLMGR -REARM and then Hit the Enter button.
Wait 5-10 seconds Now a message will appear as shown in Link image below.
Done!!! Now your Windows 7 is Genuine.. Restart your PC once. Hereafter you won't see the warning message that "Windows 7 is not Genuine"