Your system is set to UEFI mode, but your USB is configured for MBR. Recreate the bootable USB using Rufus with the "GPT" partition scheme.
If you are already running Windows and want to upgrade or reinstall without a USB: download windows 8.1 disk image file iso
Grab your product key, open Heidoc or the Microsoft User-Agent trick, and download your ISO today. For a complete visual walkthrough or updated links, bookmark this guide and check the comments below for community-driven support. Your system is set to UEFI mode, but
Since the official Windows 8.1 download page is now retired, how do you get the ISO? Microsoft still hosts the files, but they require you to go through a special workaround. Here is the safest method available as of 2025. download windows 8.1 disk image file iso