There are not too many things that prevent an iPad from charging. First make sure you are using the charger that came with the iPad and have that plugged into a known good wall outlet.
1. Bad cable. Try a different cable.
2. Bad charger. Try a different charger.
3. Dirt, lint or fuzz in the connection ports. Check and carefully clean with a toothpick if crud is found.
4. Software failure. First thing to try is to reset your device. Press and hold the Home and Sleep buttons simultaneously until the Apple logo appears. Let go of the buttons and let the device restart. See if that fixes your problem.
5. Hardware failure. Make an appointment at an Apple Store to have your device examined by a technician. Or contact Apple Support.