slmgr.vbs -ato
from an elevated command prompt
My question is : at what point does Microsoft realize that the hardware has changed, but it is still the same PC, so therefor needs to create a new hardware hash.If I remember it correctly the hardware change is considered to be a move to new hardware (like moving HDD to new PC) after 10 hardware changes.
If you have not done this (I have not done this myself yet). then you need to install the base operating system on the hard drive and upgrade it to Windows 10 (Windows 7 SP1 or Windows 8.1 are the base operating systems).