[Disclaimer]
(I take no reponsibility if you change something you shouldnt while in the registry, If you change anything other than stated here, you could hose your system.)
1. Run regedit and go to: HKey_Local_MachineSoftwareMicrosoftWindowsNTCurrent VersionWPAEvents, on the right double click on "oobetimer" and change at least one digit of this value to deactivate windows.
2. Choose run from start menu and type in this command:
%systemroot%system32%msoobe.exe /a to get the activation screen and go to the second option which is activate by phone.
3. In the new screen choose the option to change product key, erase the one thats in there and put your key back in.
4. Close that window, reboot your system and enter the command in step 2 for the second time to verify your activation , you should see "windows is already activated".
Then re-enable your network and see if that does it. If not then you should probably call the phone # in the "Activate by phone section. They should be able to get it working since its a Legal copy.