Belarc Advisor is the standard when it comes to system information software. I've been using this program for many, many years. One small aspect of Belarc Advisor is its ability to extract product keys for many software programs, including the one for Windows.
Advantages include display of information in your browser window, no adware/toolbars to worry about, and an extensive list of other important computer data.
Finds Keys for Operating Systems: Windows 8, Windows 7, Windows Vista, Windows Server 2012/2008/2003, Windows XP, Windows 2000, Windows NT, Windows ME, Windows 98, and Windows 95.
Finds Keys for Other Software: Microsoft Office 2013, 2010, (plus all previous versions), Microsoft enterprise products, most programs from Adobe, Nero, Corel, and more, as well as keys for popular video games.
Please try Belarc Advisor for your software and Windows key finding needs before any other program. It's likely to provide you with the best results.