Windows 10 pin password lock is associated with user/owner's Microsoft LiveID (Owner's email account and password).

If the mainboard is replaced, then the original PIN will not working. Because it has encryption and need to match the key value in the original mainboard's bios. 

If you try to reset the pin, Windows will ask owner's LiveID/email password.

If you want to do a full hardware test, contact customer to see if it is ok to wipe the HDD and OS reinstall (KB & Driver Update).

Or do MRI and send back the unit with HDD's original state.