I just have a black screen on my iPad

Connect you iPad to its Power Adapter (charger) and allow it to charge for at least an hour. Then, whist still connected to the Power Adapter:

• 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 an iPad with Face ID: 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 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.

If the iPad still doesn’t power-up, given that it has remained unused (and presumably not charged) for a considerable period of time, it is very likely that the battery is dead. If the battery has suffered damage from deep-discharge, it will not be recoverable.