|You have specfied Windows 7 below your user name in your the first post.|
If this is about a Windows 7 Product Key, why did you start a Topic in the XP forum ?
The latest version of keyfinder is also able to find the Product Key when the Windows installation is still there but will not load properly, as long as the physical hard drive is not failing and certain data in the Windows installation is intact.
You connect the hard drive to another computer that has the the same family of Windows running on it, e.g. an XP version if the hard drive has an XP version on it, install keyfinder and use the load hive feature in the top menu bar of it to point to the \Windows folder (directory) on your hard drive. There's some info about that in the Keyfinder FAQs on the site StuartS referred to:
If there is an official Microsoft sticker on the outside of the computer case, you can use the Product Key on that, if you can still read it, if the Windows version is the same as you already have on the hard drive, or the same as the Windows version that you want to install from scratch on the hard drive. E.g. both must be XP Pro, or XP Pro 64 bit, or XP Home, or Windows 7 Home Premium, or Windows 7 Basic, or Windows 7 whatever. For brand name systems, both are probably for OEM (full, not upgrade) versions of Windows (not retail full or retaill upgrade or Volume licensed versions) .