Power button stopped working it fall down
1) If you still have warranty then try to repair it for free.

2) You can also try to repair the ZenFone for money. But i think it will be too expensiv.

3) If you doint want to spend money the install an Power-Off-App like 
This one.
And for Wakeup you can try to install/enable Double-Tap to Wake.

I hope i could help you:)

P.S If there's an other way then let me know.