As described, something has stalled during the update.
Connect your iPad to its Power Adapter and allow the iPad to charge. While still connected to external power, try a forced-restart:
- 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. Or if your iPad isn’t working correctly after you restart it, see the iPad Support website.
If you remain unable to restart the iPad, it may be necessary to restore to Factory Settings:
If you see the Restore screen on your iPhone, iPad, or iPod touch - Apple Support
Restore your iPhone, iPad or iPod to factory settings – Apple Support
Restore all content to iPad from a backup - Apple Support
You’ll need access to either a PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS).
Download and use iTunes for Windows – Apple Support
Update to the latest version of iTunes – Apple Support
Use of a PC or Mac computer is unavoidable. If you don’t have access to a suitable computer of your own, that of a helpful friend or family member will suffice. Alternatively, the technicians at the Genius Bar of your local Apple Store or Apple Authorised Service Provider (AASP) will be delighted to assist:
Genius Bar Reservation and Apple Support Options - Apple