Have your windows expired?
Then you can read this article to get a new windows activation key and activate your system.

To get your activation key, simply goto Task Manager -> File -> Run New Task, type "cmd" inside the box that appears
and tick the box below that says "CREATE THIS TASK WITH ADMINISTRATIVE PRIVILEGES".


Now, type the following command on the command prompt without
the parethensis().
(wmic path softwareLicensingService get OA3xOriginalProductKey).
Press enter and your activation key will be displayed on your screen.