Why is ipad not turning on?

Connect your iPad to its Power Adapter and allow to charge for at least an hour. Then, whilst 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.

In addition to LotusPilot's advice, you may want to confirm that your USB cable and power supply are healthy. An old, worn out USB cable is the quickest way to get your battery to run down to the point where it will not let your device power up. And it's the cheapest of all repair bills.