Read these instructions (specifically what you must do while connecting your iPad to the computer):
Keeping in mind that if you don't have a backup all data will be lost on that device (except those that you eventually synced to iCloud), pay attention to the specific gestures that you need to perform while connecting your iPad to a computer (Windows 10 PC running the latest iTunes version) or Mac (which can run iTunes or Finder, depending on the macOS installed on it), and follow these instructions to re-gain access to your device:--> If you forgot the passcode on your iPad, or your iPad is disabled
If you still can't connect your device to your computer, see also this support article:--> If your computer doesn't recognize your iPhone, iPad, or iPod - Apple Support
Regards
Giulio