Didn't have a disc? Sounds like an OEM version installed on a prebuilt system. Typical of many of todays systems - make your own disc when you get the system which is no problem.
The Windows license is not transferrable to another motherboard. Probably as well the manufacturer has "customized" their installation of Windows to their hardware. Even if you were allowed to reuse the installation it would not work with other hardware.
Cough up the clams and buy the OS