Several scenarios suggest the change of a Windows Product Key. The IT department of an organization may have installed Windows on many machines and now wants to legitimize the install. A single Windows user might have a need to legitimize a "pirated" copy of Windows on his PC. Changing the Product Key will resolve these issues quickly and efficiently.
Installing Service Pack 1 or 2 shows whether the copy is legitimate or not. If it is not, a message will come up which states, "The Product Key used to install Windows is invalid..." Otherwise, the product volume licensing keys (VLKs) which are invalid are usually those which begin with the letters, "FCKGW-" and the IDs (which you will see on the "General" tab on the "Properties" of "My Computer" will probably have the numbers, XXXXX-640-0000356-23XXX in there, or a similar number. Either way, you will need to contact Microsoft for a valid key. If your key is valid, you can check the number in the Windows Registry and you will be able to correct it if it is wrong.
Open the Windows Registry by clicking on Start, then Run, and type "regedit" (no quotes) followed by hitting Enter (or Shift + Enter in Windows Vista.) In the regedit editor, go to: HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\Current Version\WPAEvents. You will see that there is a key called "ODBETimer" whose value will need to be changed to kick the process off. Change one of the values in the key value to a number from 0 to 9 or a letter from A to F. This invalidates the product key and will permit a change of the product key number. When you have finished altering the value of this key, close regedit.
Activate the new product key by starting the product activation software using the following command: %systemroot%\system32\oobe\msoobe /a (The path %systemroot%\system32 is equivalent to c:\windows\system32 given that the windows folder is under the c: drive.)
Choose one of three options to activate Windows: 1) Do it over an Internet connection, 2) Do the activation over the phone, or 3) Postpone it where Windows will remind you every few days. (You must activate it within 14 days or Windows will stop working). The software will provide you with an installation ID, which either goes automatically to Microsoft or which you will have to read to the Microsoft representative (if you are using the telephone system of activation.)
There are other reasons for needing to find your Windows Product Key and there are some free tools you can download to do this. One of them is the Magical Jelly Bean Keyfinder. This is the easiest tool for finding the key and you would probably want to use this if you had a pre-installed version of the operating system already loaded by the store who sold you the computer. Another scenario might be that you had a system that wouldn't start properly. This software will find the key even on a dead drive, provided the drive is accessible via a good working machine as a second hard drive.
As always with amending the Windows registry, if you do not feel comfortable about making changes to the registry, hand it over to a professional to perform. If you are unsure, always make a backup of your registry before making any changes. If you are attempting to legitimize a copy of Windows XP Service Pack 3, the software is different. Windows XP Service Pack 1 and 2 tackled the activation in the installation. With Service Pack 3, the installation has nothing to do with activation. Rather, the software, if not activated, will prompt the user to activate during the log-in screen, which is masked by a screen requesting activation. You can choose to ignore this for 30 days, after which the software stops working.