1. Hold down the Volume up button, then press and hold the Power button for a few seconds, into Fastboot Mode mode.
2. zenfone "RECOVERY", press the power button to confirm the choice by the volume keys.
Restore Factory Setting:
1. By the volume keys select "RECOVERY", then press the power button to confirm we'll see ASUS logo, such as 5 seconds (there will be a short black, normal) will see the android baby logo icon, as shown below:
Operation android after see baby icon:
Hold down the volume down button
always hold, click volume up button
then release (volume up button), [Volume Down key, always hold]
Will see the following screen, namely Recovery recovery mode, the volume buttons to select "wipe data / factory reset" press the power button to confirm.
Then automatically restore the factory settings, after the restoration is completed, automatic feed system, you will see the language settings screen.
Sumber