Given your description, your iPad battery is almost certainly failing - as all rechargeable batteries, in particular Li-ion batteries as used in iPad, must be periodically charged in order to avoid premature failure through deep discharge. Typical symptoms of a failed or failure of an iPad battery is an apparent boot-loop.
Start by connecting your iPad to its Power Adapter and allow the iPad to charge undisturbed overnight. If the problem fails to stabilise, whilst still connected to the Power Adapter, attempt a forced restart of the iPad:
- 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.
Your iPad may successfully restart - and if so, you can try disconnecting the Power Adapter. The iPad may continue to operate using battery power with reduced battery endurance, or may otherwise power-off if the battery has insufficient capacity to maintain operation of the iPad. If the iPad will not operate on battery power alone, it may still be usable while connected to its Power Adapter.
Depending upon the age of the iPad, you might consider battery replacement - although for very old models of iPad, even if battery service remains available, might not be an economic proposition. You can explore battery replacement costs here:
iPad Service & Repair - Apple Support