Download a bootable Windows 8.1 Disc.
You need a Retail Windows 8.1 key (OEM Keys will not work) and a working computer to be able to download and burn the disc. For making a repair solution if you’re using an OEM system please see this Wiki: http://answers.microsoft.com/en-us/windows/wiki/windows8_1-system/advanced-repair-tools-create-a-usb-recovery-drive/1a3ad051-1796-4238-89d8-8705e9128e24
You cannot use a Windows 8 Retail key to download Windows 8.1, not even if you have upgraded from Windows 8 to Windows 8.1 You will have to download the application for downloading Windows 8.
You cannot download Windows 8.1 or 8 64 bits on a 32 bits computer or the other way around, it will always download the same architecture of your current system
To download Windows 8.1 use this link: http://go.microsoft.com/fwlink/p/?LinkId=271128
To download Windows 8 use this link: http://go.microsoft.com/fwlink/p/?LinkID=317630
Start the downloaded application, and enter your product key at the first screen and then press Next
You will see a Window displaying the Windows version that you can download using your product key, verify this is correct and press Next
The installer will start download Windows 8(.1) this could take some time, wait for this process to complete.
Select the option “Install by creating media”
You can now choose for either an USB drive or making an ISO. If you wish to make an USB drive, select it and click on continue, then follow the instructions on the screen. If you wish to make a ISO then continue reading.
Select ISO File and click on Save
Save the file to a location on your drive and remember the location, after saving it. Then go to the directory where you saved the ISO or you can click on Open DVD Burner and skip to step 9.
Right click on the ISO you just saved and select Burn disc image
Insert a blank recordable disc in your burner and click on Burn. (The instructions on the screen will help you further.)
How to boot from the disc
First, ensure you BIOS is set to boot from a DVD device, then put the Windows 8(.1) disc in your system and press on a random key when this message appears