Ensure that iTunes has been updated to the most recent version. If you have a recent model iPad, you will require either a Windows 10 or Windows 11 PC.
If your iPad is still not recognised when connected, try using a different USB port. Otherwise, this support page should help with troubleshooting connection issues:
If your computer doesn't recognize your iPhone, iPad, or iPod - Apple Support
If you continue to experience difficulties, you might be well advised 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, if you have access to another Apple device, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed, 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 assist:
Genius Bar Reservation and Apple Support Options - Apple