If the battery was completely discharged the iPad may take some time to respond. But if you are seeing stuff on your screen then there must be some juice left.
Couple of things to try.
1. Make us you are using the correct charger, the one that came with your iPad. Un plug all the connections and plug them in again making sure they are in securely.
2. Next thing to try is a reboot of your iPad. Press and hold the Home and Sleep buttons simultaneously ignoring the red slider until the Apple logo appears. Let go of the buttons and let the iPad restart. See if that fixes your problem.
3. If you still can't get the iPad to charge you can try a different charger and cable if you have one available. If you can't do this I'd visit the Apple store and have them look at it.