Asus X200LA - Manual (Page 100)

100 Notebook PC E-Manual
6. How can I boot to DOS using my USB drive or ODD?
Refer to the following steps:
a. Restart your Notebook PC and enter BIOS by pressing F2 on
your keyboard.
b. Go to Boot > Launch CSM > Enabled.
c. Go to the Security menu then set Secure Boot Control to
Disabled.
d. Press F10 to save changes and exit BIOS.
e. Press and hold ESC to launch boot menu when your
Notebook PC restarts.