I have seen my fair share of people struggle to get their computers to boot from USB drives, and I was no exception. My Toshiba L875D-S7135 notebook computer would not boot from any USB drive, regardless of what I did. There are multiple causes behind this problem, especially settings.
Possible Causes/Fixes
- Adjust the boot order in your computer’s BIOS or UEFI settings. Otherwise known as a setup utility, that settings screen is not a part of your computer’s operating system, and will allow you to make some risky changes to your computer, so be careful. Ensure that ‘USB’ and ‘ODD’ (or whatever it calls your optical and USB drives) are above the HDD. That will make your computer check them first before trying to boot from your hard drive.
- Enable USB Legacy Emulation.
- Ensure that the operating system on the USB drive is UEFI compatible. You cannot boot a non-UEFI OS on an UEFI machine (if your computer is configured boot to UEFI only). Older machines use the Master Boot Record (MBR), and modern machines use UEFI firmware instead.
- Some operating systems don’t support with the Secure Boot feature turned on. Secure Boot checks for a digital signature before booting. If it doesn’t find one, you won’t be allowed to boot the OS. This prevents Ubuntu from booting (at least, version 14.04).