Just build a 9900k system and have windows resdy on USB and i can’t find the option to boot to it, someone maybe knows pls?
GIGABYTE GA-78LMT-USB3 USB devices do not work, and can not boot from USB flash drive?
Gigabyte UEFI boot
Gigabyte motherboard won't boot from USB
Can't boot from USB on Gigabyte Motherboard
Videos
The answer was extremely simple. @oldfred provided it with his comments to this question. The boot device (after hitting F12 to bring up the boot menu during Post screen), turned out to be the Sandisk Cruzer listed first under +Harddisk table.
I had never entered that part of the boot devices screen. I had only looked at USB devices. Booted right up from the Flash drive (USB Sandisk Cruzer).
After hours of frustration and reading every forum & blog I could find I have the solution. On the latest Gigabyte MB's like the H370M D3H you have to enable CSM Support. Once you do that viola, all USB drives are recognised at boot and Will launch the boot process.
Use Plop Boot Manager.
Materials
2 computers
1 computer with the problematic (GIGABYTE) motherboard
1 computer for write operations to flash drives
2 USB FDDs
1 (tiny capacity) flash drive for Plop Boot Manager
1 (larger) flash drive for the anticipated boot disk
1 open USB slot
Setup
- Download Plop Boot Manager. Get
plpbt-x.x.x.zip(wherex.x.xis the latest version number). - Extract the
.zipfile you downloaded. - In the folder resulting from the extraction, find
plpbt.img. Unmount your tiny FDD.
Write the file (Plop Boot Manager) to the beginning of your tiny FDD with this:
Linux:
sudo dd if=plpbt.img of=/dev/sdnMac:
sudo dd if=plpbt.img of=/dev/diskn(Assumes that you changed directories (
cd plpbt-*) into the extracted folder. Replace the value of theof=parameter with the path of your particular flash drive. Be careful with this command by checking it for correctness!)Windows: Use Win32 Image Writer to write the
.imgfile.- If you haven't already, write the bootable operating system to your other flash drive like normal.
Usage
Plug the Plop Boot Manager FDD into the computer with the problematic (GIGABYTE) motherboard.

Reboot or power on that computer. On GIGABYTE motherboards, press F12 at the BIOS splash.

Select the Plop Boot Manager FDD for booting. On GIGABYTE motherboards, choose either
USB-ZIPorUSB-HDD. The flash drive is actually recognized as a floppy, not a regular flash drive.
- Plop Boot Manager should now be running. There may be a starfield screensaver in the background.
- Plug in the other FDD. (Exchange with the Plop Boot Manager FDD if you're out of slots.)
Select the flash drive option from the Plop Boot Manager menu.

Now the bootable flash drive operating system should be starting up!
As a bonus, there are other uses for your Plop Boot Manager FDD now, and it can be your "key" to other possible booting issues you might encounter.
- In the BIOS, ensure you have Integrated Peripherals > USB Legacy Enabled.
- Also ensure you have Integrated Peripherals > USB Storage Enabled.
- Set Boot Order to HDD, None, None.
- With the USB Boot Drive inserted, Reboot.
- Hit F12 at the Boot Screen to bring up the Boot Menu.
- Choose HDD+ on the Boot Screen, not any of the USB options!
- Choose your USB Device on the next screen.
Source: http://forums.tweaktown.com/gigabyte/24883-welcome-gigabyte-technical-support-133.html#post394471
HOURS of research - I hope this helps.