Loosing your Microsoft Windows product keys is very annoying as you cannot reinstall those products anymore in any circumstances. But unfortunately reinstallation is very common. Sooner or later, you will find yourself upgrading to a new computer with a larger hard drive or encountering critical Windows failure and system error that both require you to reinstall all of the applications that you need with its valid product keys. The easiest way to retrieve your lost product key is by using a key finder software.