Some questions about operating systems

[yeti_yeti]

I built my pc 3 months ago and installed a 90-day "trial" version Windows 8.1 in it. It is going to expire in few days. My questions are:
-Where can I get license key to activate it back, once it expires?
-Are there any way to get full OS versions legally for my future builds?
Im sorry if those questions seem completely retarded, Im just very poorly informed on this specific topic
Any help is appreciated

 

[SoggyTissue]

Does the trial version not come with a nice toast pop-up with the link to 'activate/buy windows now' link? sometimes hidden on the system tray as an icon. Else you could probably goto the microsoft site, create an account and buy it through that like how office works now.
Youre really buying the key (rights to use) whatever version youre looking at. It usually comes with a small print term: one user licence/only usable 3 times.

 

[yeti_yeti]

Does the trial version not come with a nice toast pop-up with the link to 'activate/buy windows now' link? sometimes hidden on the system tray as an icon. Else you could probably goto the microsoft site, create an account and buy it through that like how office works now.
Youre really buying the key (rights to use) whatever version youre looking at. It usually comes with a small print term: one user licence/only usable 3 times.

Im currently away from my home and unable to check whether or not my pc will link me to the site, where I can purchase the OS upon expiration. Im really sorry for another probably stupid question. Since upgrading a motherboard will require you to reinstall windows, would that mean that I would have to purchase it again if i buy a new board?

 

[SoggyTissue]

Installing a new mobo doesnt require a fresh windows install. I cannot vouch for windows 10.
Changing your hard drive may do if you dont use a drive imager.