My laptop had windows 8 preinstalled and then i installed ubuntu 14.04. But now I want to reinstall windows 8 and dual boot the two but I don't know how to get my product key or get the windows 8 iso file. I heard that windows 8 has the product key in the BIOS but I don't know how to access it to download the windows 8 iso file. Do I have to purchase another copy of windows 8 in order to do this ?
Be careful! It can be dangerous to install Windows after some other OS. The Win bootloader might mess up your partitions:
A Windows OS should be installed first, because its bootloader is very particular and the installer tends to overwrite the entire hard drive, wiping out any data stored on it. If Windows isn't already installed, install it first. - quote: help.ubuntu.com
The easiest and safest way is to reset the computer to its original state and then install Ubuntu as dual boot.
If a PC has Windows preinstalled and no backup-cd shipped with it, there usually is a backup software included. If not, you should be able to get a free backup cd from your vendor. A very useful site about all this is here: https://help.ubuntu.com/community/WindowsDualBoot