For Windows10 ASUS computers, to boot from a USB drive you need to change the Boot prioirty in the Bios.

To get to the BIOS...

STEP1: Hold SHIFT + Shutdown

boot from usb1

Step 2: Hold F2 + power button

boot from usb2

STEP 3: Change the Boot Priority in the Bios.

boot from usb3

Reference:

http://www.asus.com/support/faq/1013015/