Several websites have posted this Windows 7 how-to which basically extends the trial period to 120 days without needing an additional key. And because we love to keep you updated as much as possible, we will teach you how to easily extend your Windows 7.
The main point of this hack, if we can call it like this, is to run “Command Prompt” as an Administrator. Find the “Command Prompt” link, which usually is present within Start >> Accesories or just write “command” within the search field and it will be filtered in the same windows. Now, right click on the “Command Prompt” link and click “Run as administrator”. The command prompt console will be pop-up and you need to write the following command: “slmgr -rearm”
You will receive a pop-up notification that the command completed with success and at this point, you only need to restart your system. Enjoy your extend copy of Windows 7.