can you run windows on old hardware still? if so, do this before swapping -
reactivating win 10 on new hardware
sanest way to do it after a new motherboard is a clean install.
On another PC, download the
Windows 10 media creation tool and use it to make a win 10 installer on USB
change boot order in BIOS so USB is first, hdd second
boot from installer
follow this guide:
http://www.tenforums.com/tutorials/1950-windows-10-clean-install.html
when you reach screen asking for licence, click "I don't have a key" and win 10 will continue to install and once its finished, follow my 1st link above to reactivate it
On the screen where you choose where to install win 10, if it gives you an error about GPT drives, delete all the partitions on the hdd and press next. If it still gives error, cancel out of the installer and restart PC and start installer again, it will accept next on that screen this time (some PC just need a restart here)