My iPad Air is turning off by itself and it turn on when it wants

What can i do to fix my iPad Air?It turn off by itself and it will not turn on again only after hours or even months.This problem appeared 6 months ago and since then the ipad come back to life 4 times,first 2 after 1 day and the third time the ipad turned on after 4 months (a week ago),and the fourth now.What could be the problem?