Thank you for using Apple Support Communities.
It sounds like your iPad, although plugged in, is not charging.
Based on this aricle, it seems like the USB port you have it plugged into is not providing enough power to charge the iPad.
iPad: Charging the battery
Note: Some USB 2.0 ports and accessories do not provide enough power to charge iPad. When this occurs the message "Not Charging" appears in the status bar next to the battery icon.
Try plugging it into the power adapter that came with it and see how that works.
Also you may want to try restarting the iPad:
iOS: Turning off and on (restarting) and resetting
Or even resetting the iPad:
If your device stops responding, you can reset it by pressing and holding both the Sleep/Wake and Home buttons for at least ten seconds, until the Apple logo appears
All the best,