ms's rule: one key can only be used on one computer.
the genuine key supports many and many re-installation as you want(but unexpected thing always happens).
actually, the key is bound with the motherboard. if motherboard is changed, the old key will not work any longer. so don't change the motherboard unless you have to.
a little use to contact ms under such condition.
backup is a very important method to avoid such accident. keep good habit to backup your computer.
in case, you lose the original key, or have to change the motherboard, or no backup, you must feel unfair to buy a new key at that cost from ms online store.
here suggest to buy a key from a msdn partner. their price is much cheaper, under the acceptance. you can search
REDACTED - SSon google. good luck!