I have been trying to install an ISO copy of windows 7 to my Asus vivobook Max A541U. The stock OS was windows 10. I wanted to downgrade it due to some issues. I mounted the ISO on the USB drive with Rufus tool first with the gpt format with UEFI boot mode. Then went into the BIOS disabled fast boot and secure boot, switched on legacy mode. When the installation started up the first error was " a required CD-DVD driver is missing". then i searched the net for solutions, after which i found gigabyte USB installer. Here comes the other mistake. with the Gigabyte USB installer, i mounted it MBR partition. (i don't really remember this step, i did something and mounted the ISO in MBR format using the USB). Then i rebooted, booted using USB, then after language selection another error came. "cannot install windows to this disk as it is gpt partition". Then i accidently format my C drive. where my OS was located. Then ever since i cannot install this windows 7 because the first message after startup is "required CD-DVD drive missing". Tried everything i could. I need help!!! http://codeabitwiser.com/2014/03/how-to-install-windows-7-with-only-usb-3-0-ports/ even tried this! wim mounting or something. I have a laptop with no OS XD...... PLEASE ANYONE!!!!