Microsoft’s 30 Day period is an understandable precaution to protect Microsoft’s software, but if you accidentally go over this period before activating or you have just restored your computer from an image running OEM software, you can find yourself in a bit of a catch-22. If you go over your 30 days without activation or if you get a message stating you must activate to login again, try this:
1. Turn On your PC
2. Press F8 repeatedly and go to Safe Mode
3. Logon as normal ( as an administrator )
4. Allow the Desktop to fully load
5. Go to a command prompt
6. Type in exactly:
and then hit the enter key (Note: this command is case sensitive)
7. Wait about 10 seconds (although you should not see any changes or messages)
8. Restart your PC normally (Start, Shutdown, Restart, Ok)
9. You are now able to go to Normal Mode again (You have just reset it for another 30 days and have removed any bios locks)
That is some kind of offical way to reset the Activation Trial.
It will work only work for about 4 times.
Do not use on an already activated PC (as it will force you through the re-activation process again )