iPad power button is not working

If your iPad or its Top (Sleep/Wake/TouchID) button is unresponsive, connect your iPad to its Power Adapter and allow the iPad to charge. Then, while still connected to external power, try a forced-restart:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

If you continue to experience difficulties, you will need to seek assistance directly from from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/gb/app/apple-support/id1130498044

You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad:

Genius Bar Reservation and Apple Support Options - Apple

That's a hardware issue, you'll need to call Apple Support or setup an appointment at an Apple Store or Apple Authorized Service Provider:

Genius Bar Reservation and Apple Support Options - Apple

Contact - Official Apple Support