First try a hard restart - hold down the power button and home button for around 10 - 12 seconds. If that doesn’t work, plug the device into a computer and hold down the two buttons again for 15 seconds. If you still get no response and the device is still under warranty, take it back to an Apple store to get it looked at. If it’s not under warranty, a battery and screen replacement would be where I’d start followed by a charging dock replacement