Rearm Windows from Evaluation Period

If your 30 days trial is about to expire, I found a good way to rearm it. I have learned this quirk and I just wanted to share. Here's how to do that:

1) Run your CMD as Administrator.
2) Type slmgr.vbs –rearm
3) Restart your system and smile. :P

If the above command didn't work, specially if you're using Windows 7, try:
slmgr.vbs /rearm

Have Fun! :)