Log in Administrator ( to be able to edit registry )
Click Start > Run > Regedit
Go to HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\wpaevents
In the right pane, right-click OOBETimer, and then click Modify
Change at least one digit of this value to deactivate Windows
Click OK and close regedit
Click Start > Run and type in: "%systemroot%\system32\oobe\msoobe.exe /a"
Click Yes, I want to telephone a customer service representative to activate Windows, and then click Next
Click Change Product Key (at the bottom)
Enter your valid Corporate Product Key
Press Update and close the window.
If you are returned to the previous window, click Remind me later
Restart your computer