Once the download is complete, you cannot simply copy the file to a USB drive. You must "burn" it to create bootable media. Using a USB Flash Drive
Here is a comprehensive review of the download and the OS itself. microsoft windows 8.1 download iso 64 bit
Backup all important data before performing a clean install. Download the ISO only from . Have your Product Key ready. Create a bootable USB using a tool like Rufus . Once the download is complete, you cannot simply