If you have lost your Microsoft Windows XP/Windows Vista Serial key number then here are some solution to retrieve the serial number. For Windows xp users if you have your original CD with you then Insert WINDOWS XP CD into the player and Just explore the cd to find a folder called i386 where you will have a file unattend.txt.
Open the text file and you will find the CD serial key of your Windows Xp when you scroll to the bottom, use the serial key and make sure you save the license number on a paper as well, just to be on the safer side.
Another solution for most of the Microsoft product keys is to use 3rd party applications such as key finder which is a small executable file searching the windows registry to gather serial keys instantly.
Keyfinder is one such freeware open source utility which is the easiest solution to retrieve your Product Key (cd serial key) and also saves the serial keys of un bootable Windows applications in text or csv format. Key finder 2.0.1 works with Windows 95, 98, ME, 2000, Windows XP, Server 2003, Server 2008, Office XP, Office 2003 and the latest update supports Windows vista, so retrieving the lost key can be done through the registry files automatically by such freeware software. Download Keyfinder v2.0.1
Another free utility is License Crawler which not only searches for Microsoft Windows product keys but also does a high speed scan of various installed software’s retrieving a bunch of serial keys in quick time. Hopefully these ideas will help you to retrieve the lost serial keys and as a note – Always make sure you save and make multiple prints of your serial keys using above method to be on the safer side! I hope the solution helps whenever you have lost the Microsoft Windows original CD.