How to boot from a CD on windows 10?

[Lawk Duski]

Hello, So my bro bought an Asus N551Z Laptop 2 days ago and it has windows 10 in it, the problem is its not genuine, nor the windows CD or anything else is with it, now I have windows 7 ultimate and windows 8.1 Disks, both 64 bits, I want to install windows 8.1 on it from a CD but the problem is it doesn't boot, like the laptop starts and after the "Asus" logo it doesn't tell me "Press any key to boot from CD", why is this? how do I boot from CD when you start the laptop on windows 10? it worked on my other laptop with windows 7 on it, it does tell me to press any key to boot from CD and so I proceed to install windows 8.1 on it, but why doesn't it allow me to boot from CD while using windows 10? I checked bios, its all correct, boot from CD ROM is first priority and everything, and i did try to run it from my computer like open the installation manually but it gives me an error, i need help asap, how do i boot from CD when the laptop first starts?
Thanks

 

[drmosko]

go to - http://www.asus.com/support/FAQ/1008829/