depends if it is OEM, you can only install it in one machine only. You must not use it in other pc, it is like that OS is married to that Machine. If the pc brokes down like the MOBO is dead, once you replaced it, it will deemed new and it is considered void already and you must buy another license for it. Components lang gyud like video card, hdd etc and puwede nmo ma add yata. Kung ma dead na, dead na pud ang license. It is not transferable, i think, puwede ma transfer kung volume license. i don't know much about volume license nila. What i don't like about Microsoft is they have this country restrictions sa licensing, meaning if you buy it from the US, you can't use it here in the Philippines. They have specific install or OS that has For Philippines only. Which is a total bullcrap to me, because the price here is way to high than buying it outside this country.
Grabe ka pangwarta no.