When you install Microsoft Windows, you have to enter a product key in order to activate it. The product key is a series of letters or numbers and is provided with your computer or the Windows software. There are applications that will delete the Windows key, but you can do so by entering a simple DOS command.
1. Click “Start” and type “cmd” in the Search box, then press “Enter.” A black window will open.
2. Type “slmgr –cpky” and press “Enter.” Wait for confirmation.
3. Click “Start,” the arrow to the right of “Shutdown” and “Restart” to restart the computer.
Into Windows: Delete Windows Product Key from Registry
Source from RitaW, eHow Contributor