Are you using the included power brick and plugging it into the wall?
have you given your device a reset. Hold down the sleep and home keys until you see hte silver apple. Let it reboot and try again.
If you're trying to charge from USB it doesn't work well. Most USB's don't provide enough power to keep the iPad happy.
Generally charging issues can be traced back to four causes:
Bad power brick
If you can swap those out you can either confirm or rule out those causes then the last thing is that the port has issues. If that's the case then you may need to take it into the local apple store and have it looked at becuse if there is something with the port, it's beyond a user fix.