“Generally, you may upgrade or replace all of the hardware components on your customer's computer and the end user customer may maintain the license for the original Microsoft OEM operating system software, with the exception of an upgrade or replacement of the motherboard. An upgrade of the motherboard is considered to result in a "new personal computer" to which Microsoft OEM operating system software cannot be transferred from another computer.
If the motherboard is upgraded or replaced for reasons other than a defect, then a new computer has been created and the license of new operating system software is required.
If the motherboard is replaced because it is defective, you do NOT need to acquire a new operating system license for the PC.”