How to turn old iPad on after not being used for years
Please try the hints &amp; tipps of the web page I added the link at the end of my answer.

I recommend starting with the "hard reset" as this might help if the iPad just got "stuck": 
"perform a hard restart by pressing and holding both the HOME button AND the POWER/SLEEP/WAKE button until the Apple logo appears."

If it is sure that the iPad got charged and you don't see a symbol about "low power", and if the hard reset didn't help it might be necessary to connect the iPad to a Mac or PC with iTunes installed. Please continue with the instructions of the linked page.

If this is not the right direction for you it might be an alternative to just find help either by Apple Tech guys in an Apple Store or in some stores where Apple iOS/iPads is well known stuff...

Here's the link:
http://appletoolbox.com/2014/12/ipad-will-not-turn-fix-dead-device/

Good luck! Fingers crossed.