My phone Screen blackout while working on phone and not wakeup for few minutes to wakeup the phone the power switch is also not working, kindly resolve the issue
Your best option is to do a factory reset and see if that solves the problem. Otherwise you might need to return the phone to an Asus service center.
Are you on the latest firmware?
It could be a hardware problem, do visit your local ASUS service centre if you are unable to do a factory reset or a factory reset does not solve your problem.
I found a similar issue on XDA
You might want to take a look.
Have you tried the fix suggested from the xda thread? If it worked, then please let us know if this ever happens again