So far, trying to boot from a USB thumb drive on my Toshiba L850D has been an abject failure. The steps I followed here have leave the laptop in a state where it still won’t boot off the thumb drive, but also fails to boot Windows off the hard disk. It is possible to boot off the DVD drive.
The Toshiba L850D BIOS access is truly horrible. The process to have the laptop boot off USB that I’ve pieced together, which has left the laptop in a disfunctional state, is this:
- Power the laptop off.
- Hold down the Fn and F2 keys
- Power the laptop on and hold the keys for a second or so. The machine will then boot to an Automatic Repair menu.
- Select See Advanced Repair Options
- Select Trouble Shoot
- Select Advanced Options
- Select UEFI Firmware Settings
- Select Restart. The laptop should reboot into the BIOS settings screen
- Select Boot on the top menu (using the left arrow key)
- Select USB (using the down arrow)
- Move USB up in the boot order by pressing the F6 key
- Select Security on the top menu
- Select Secure Boot using the down arrow and press F5 to toggle its value to Disabled
- Select Advanced on the top Menu
- Select >System Configuration using the down arrow, the press Enter
- Select Boot Mode using the down arrow and press F5 to toggle its value to CSM Boot
- Press F10 to Save and Exit and Enter to confirm
Here is one source I followed: http://www.tomshardware.com/forum/64755-63-toshiba-satellite-boot
I’ve read that you can completely reset the BIOS by removing the CMOS backup battery. This did not work for me. After trying this, the laptop still refused to boot from the hard drive. I believe it is because the CSM Boot is still enabled.
Note: After setting it to boot in CSM mode, you can no longer enter the BIOS with Fn-F2. Instead, press F12 at boot and you’ll get a boot menu with an option to change the BIOS configuration.
I finally gave up and booted the laptop off DVD by selecting the correct option from the boot menu. Note that after booting the LMDE2 installer, the track-pad and keyboard did not work unless boot mode was set to CSM Boot.