iPad Pro

If iPad isn’t responding, do one of the following:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On other iPad models: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

Note: If iPad still doesn’t turn on, or if it gets stuck during start up, see the Apple Support article If your iPhone, iPad, or iPod touch won’t turn on or is frozen.

If you're sure you followed ALL these steps:

• On an iPad with a Home button: Press and hold the top (power) button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On other iPad models: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top (power) button. Only when the Apple logo appears (it might take 20-40 seconds), release that button (ignore all other screens that might appear).

and, if the issue persists, contact Apple Support, using this link:--> Get Support

Regards

Giulio