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
Step 2: Hold F2 + power button
STEP 3: Change the Boot Priority in the Bios.
Reference:
http://www.asus.com/support/faq/1013015/