extend the activation period to the maximum 120 days instead of the 30 day of win7

run slmgr -rearm to get another 30 days at an administrative level command prompt.  You can do this a maximum of three times before Microsoft blocks further extensions.

1. Click on the Start Button and type in Command. 
2. The Command Prompt Prompt shortcut will now show up in your start panel search results. Right click on the shortcut and select Run as Administrator.
3. After Command Prompt loads, type in slmgr.vbs -rearm and hit Enter.
4. Reboot.