"As for the license, surely it pertains to my mobo? Wouldn't it be the same as reinstalling Windows?"
The licence doesn't just cover the motherboard, there are other restrictions too, one of which is that you can't use the same licence/product key to install a second copy of Windows unless you wipe the existing Windows first (or immediately afterwards). That's not the same as re-installing Windows at all.
When you reinstall Windows you overwrite the one that's screwed up, so you still end up with just one Windows installed, which is quite legal.