How to turn on my iPad Air 2
Did you try connecting it to the charger? The battery may have run out of charge. Leave it plugged in to the charger for half an hour and then try turning it on again.

It's recommended to follow the steps outlined in this Apple support document, If your iPhone, iPad, or iPod touch won‘t turn on or is frozen.

The last resort would be to get in touch with Apple Support or get it inspected by an authorised Apple technician.