There aren't too many things that prevent an iPad from charging as long as you are using an Apple 12w charger and original Apple or name brand Lightning connector.
1. No power to the outlet. Check to make sure outlet is live.
2. Bad charger. Try a different charger.
3. Bad cable. Try a different cable.
4. Dirt, lint or fuzz in the connection port on the iPad or the charger. Check and carefully clean if necessary.
5. Software failure. Reset the iPad. Press and hold both the Home button and the Sleep/Wake button continuously until the Apple logo appears. Then release the button and let the device restart. You will not lose data doing this. It's like a computer reboot.
6. Hardware failure. Make an appointment at an Apple Store to have a technician examine your device. Or contact Apple Support.