dgingeri :
You'll still need a product key no matter what method you use.
Moving from one system to another is only available from a retail license with Windows 7 and up. An OEM license is locked to the motherboard permanently. If you have an OEM license on your old machine, then you can only buy a new one for the new machine. It's as simple as that. If you have a retail full version, then you can move it to other machines, but you can only have one active at a time.
This is absolutely nonsense. If you have upgraded (or bought a key) to Windows 10 from earlier OS(Win 7/8/8.1) you don't have to buy a new key if you install windows 10 on a new machine. If you had some knowledge about how Windows 10 works you wouldn't post this rubbish.
In Windows 10 you have the option to link your Windows 10 license to your Microsoft Account (digital license). And when you buy a new computer or motherboard and CPU, the only thing you have to do when installing windows 10 is to fill in your Microsoft account details (email and password) and your Windows will be activated automatically.
This method works only if you have linked your license to your Microsoft account.
Here is how to link your digital license to your Microsoft Account:
http://www.windowscentral.com/how-link-your-windows-10-product-key-microsoft-account
Remember to read this carefuilly on the same page:
"Starting with the Windows 10 Anniversary Update, your product key is no longer only attached to your hardware — you can also link it to your Microsoft account. This new change allows you to re-activate Windows 10 without having to contact Microsoft when you make significant changes to the hardware on your PC, including replacing the motherboard, processor, or hard drive."
Please get some knowledge about how Windows 10 works before posting useless advise.