For those wondering why it’s so bloody difficult to boot from a thumb drive with Windows 8 or Windows 10.
One reason: Microsoft is trying to protect you from yourself.
That said, a caveat is in order. The following procedures are documented from testing with an ASUS Model X200M (laptop) running Windows 8.1. Your BIOS screen may differ as may the keys required to access the BIOS and the boot menu.
Park the USB
Since the procedures involve restarting the computer and pressing keys to intercept the automagic boot from the hard drive, it is best to prepare by inserting your bootable thumb drive in an available USB port ahead of time, rather than scrambling to plug it in during the boot process.
As Needed
The following procedure is conditional, based on the current settings for the two specified options. Once these changes are made in the bios, they will be retained until such time as they are again changed, whether deliberately, by accident, or through failure of the battery supplying charge to the CMOS. If you have already made these changes, move to the next section, “Every Time”.
- From powered down state, turn on the power OR, if already in Windows, choose Shut Down, Restart.
- Then immediately press and hold the F2 key or Del(ete) key (to enter the BIOS settings).
- When the BIOS settings page appears, go to the “Boot” tab (press right-arrow key twice).
- From the “Boot” tab, under “Boot Configuration”, check the setting for “Launch CSM”. If it is set to “Disabled”, press the Enter key, to change it. If it is already set to “Enabled”, skip to step 7.
- Choose the setting “Enabled” (up- or down-arrow key).
- Press the Enter key.
- Go to the “Security” tab (press right-arrow key once).
- On the “Security” tab, at the bottom, choose “Secure Boot Menu” (press up-arrow key once).
- Press the Enter key.
- If it is set to “Enabled”, press the Enter key, otherwise skip to step 13.
- Change the setting for “Secure Boot” to “Disabled” (up- or down-arrow key).
- Press the Enter key.
- If you changed either setting, press the F10 key, and then the Enter key, to save changes and exit. Otherwise, just press the Esc key twice, and then the Enter key, to exit without saving changes.
- Press and hold the Esc key, as the computer restarts, to access the Boot menu. However, see the “NOTE”, below.
Every Time
The second part is performed each time booting from USB drive.
Presuming that you have performed the one-time procedure above, and Launch CSM has already been set to Enabled, and Secure Boot has already been set to Disabled, and that your bootable USB flash drive is already inserted in an available USB port, on power up or restart, press and hold the Esc key to access the Boot menu.
NOTE: Sometimes, on a restart, particularly from the BIOS settings, the computer will ignore the pressed Esc key and boot into Windows anyway, in which case, release the Esc key, choose shut-down, restart, and try it again, pressing the Esc key as soon as the blue “Restarting” screen appears and hold it down until the boot menu appears.
When presented with the Boot menu (“Please select boot device:”), you will typically see two entries indicating your USB bootable drive, one prefaced with “UEFI:”. Choose the other one, and press the Enter key.
And Bob’s your uncle.