Windows Vista/Activation

As with all versions of Windows released since, Windows Vista requires product activation with Microsoft’s servers. This process permanently links the product key entered during setup to the PC you installed it on. Once a copy of Windows was activated, that product key would no longer function on any other computer. If a user tried to activate Windows on a different computer following successful activation elsewhere, an error would be displayed. Note that this does not impede reinstalling Windows on the same computer, if you have purchased a full version and not an upgrade disc. (If you installed Windows on a blank partition using an upgrade-only disc, Windows would refuse to activate.) Microsoft requires in the license agreement that all installations of Windows Vista be activated.

The grace period
When installation is completed, the system will start a 30-day grace period in which the computer will run and be fully functional without activation (although it will display pop-ups reminding the user to activate). At the end of this period, Windows would enter Reduced Functionality Mode (except if successfully activated). In Reduced Functionality Mode, Windows would present non-closable windows every hour, on the hour, complaining that the computer has not been activated. Access to other features may also be blocked. (Windows also enters Reduced Functionality Mode following an attempted activation if the product key used during Windows installation did not match the edition installed, or if the product key was already activated on another computer.)

SLMGR.VBS
There is a fully supported technique that resets the grace counter on an unactivated copy of windows to a full 30 days. This can be successfully performed up to three times. To do this, the user would open an elevated (Administrator) command prompt and run the command, and then reboot. This program can also be used to activate Windows from the command line, change the product key used on an existing installation , and various other functions.

Windows Anytime Upgrade
Windows can be upgraded from certain editions to certain other editions through purchasing an upgrade disc through Microsoft’s Windows Anytime Upgrade program. The process is identical to installing Windows Vista as an upgrade install. Note that Windows Anytime Upgrade requires a second, different product key. If the original product key used to activate the old edition was entered, Windows would fail to activate.