Zenfone 5 A502CG Unable to enter fastboot/droidboot

Hi all,

I'm not very familiar with phone terms but the situation is like this:-
- suspected like bricked
- connect USB to computer and press Volume Up + Power = USB Logo with white load bar
- disconnect USB and turn on = Repeatedly show Asus logo
- disconnect and press Volume Up + Power = USB Logo with red bar with a splash off Asus logo and turn off (a blink an eye)
- real problem is unable to enter droidboot/fastboot

I have tried to search for the thread to solve this problem but not successful yet. Method that I have tried so far:-
- installing iSocUSB
- installing Intel driver
- installing xfstk (FW+OS failed)
- installing MFT (not know which file that be used as zip/xml)
- run adb tools command (error: device not found)
- Intel SOC appear on device manager and when connect the phone to USB, it will appear CloverView too.
- installing asus pc link
- installing PDANet

I have seen most thread and discussion mention a phrase like "press volume up + power and you will enter fastboot/droidboot" but how about IF I can't enter fastboot/droidboot; they not mention the step. What should I do to enter it? I also search for key "A502CG unable to enter droidboot/fastboot" but result from google shows as what I mention before; the phrase "press volume up + power and you will enter fastboot/droidboot" which not working on me.

If someone has same problem with me and solve this to recover the firmware to its origin, kindly share. I believe there is someone who are same as my situation here.
Hope for help/guide. Thanks