Hello and welcome to the forum.
First.... This is a technical "Preview" version of the OS and not something you would want to install as your primary OS on you primary machine. It is available for testing and evaluation and will expire.
Second.... Any product key you currently have is for the "Preview" version of the OS and will not be valid for a General Availability Release later on.
Third.... I've installed every build as it has become available and have never been prompted once for a product key.
Finally.... If you want to play with this version, my suggestion would be to do so inside a Virtual Environment (using VMware Player or VirtualBox), or on a second inconsequential machine.
