This was crucial for me since there was a computer I was trying to reformat for a customer and the original hard drive could not boot with a different motherboard, as the original motherboard was toast, and Windows Vista product key on the side panel of the computer case was worn, making the the serial unreadable. So I reinstalled Windows Vista onto another hard drive in hopes of Google searching something that would be a solution. Of course I was able to instal Vista without being prompted for a serial until I was to look for updates with Windows Update, I had to “Activate Windows”, which cannot be done without the serial of course.
I found something, as usual.
So this is what you do once you are boot into Windows, and I think this will work for any version of Windows. Comment on this post if this doesn’t work for you.
1) Go to Start, and click on Run. Type in CMD, press enter. (you will see that “Run” window above, showing you where to type “CMD“).
2) Type in C:\>find /i “ProductKey” E:\windows\system.dat
If the drive letter of the secondary hard drive is different than “E“, then change it to the actual letter of your secondary hard drive. Now it should show the key to the Windows installation on that drive!.
Hope that helps all of you guys out there.