I restart apple ipad several times but it screen remains unresponsive.

Start here >>> If the screen isn't working on your iPhone or iPad - Apple Support

If your iPad is unresponsive, 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.

If the iPad 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 continue to experience difficulties, you will need to seek assistance directly from from Apple Support. You can contact the Support Team using the Get Support link at top-right 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

For much newer design iPad models, without a Home button, try the new simple hard reset procedure for the new 2018/2020/2021 iPad Pros, 2020 iPad Air 4 and 2021 iPad Mini 6 models.

1. Press and release the volume button closest to the top Power button

2. Then immediately press and release the volume button farthest from the top Power button.

3. Then, press and hold the top single sleep/wake/power button You will see the Slide to Power off button, but keep on holding down the power button until you see the Apple logo, then let it go.

Once you have performed all the steps, wait for a few seconds and your 2018 iPad Pro will boot up completely to the iPad Pro’s Lock screen.

If this is a fail,

It maybe time to use the “Get Support” link, at the upper right hand corner of every Apple Support Community Webpage to attempt to schedule an appointment with your nearest Apple Store location to have your iPad diagnosed by Apple employees and options presented to you.

Apple Store employees will be glad to help/assist you.

Best of Luck to You!