phone cannot be switch on and battery draining too fast

holla. i am an asus user. i confused and get some worries when my smartphone drained the battery power very fast. why ?

and one more, my smartphone asus zenfone 2 cannot be switch on after suddenly the battery 15 % left ? please help me . as try to charge it and switch on, but it doesnt work ! please. i am begging . as i didnt play my phone since 2 months ago. honestly, i felt quiet difficult as my data and social apps are in it.