AntonyGA,
Which is why people who build their own computers are not permitted to use OEM licenses.
Microsoft are quite clear on that, see
Licensing for Hobbyists
They are also similarly clear that if a motherboard is upgraded or replaced, for reasons other than a defect, then a new computer is created and OEM license is void.
Think about it, it makes sense. The metal chassis is just that, it has no functional use .... the motherboard is what makes the computer what it is.