Hi, welcome to iPF!
Does the iPad show anything, like "Not charging" at the top right, next to the battery icon, or do you see any popups on the PC?
If everything else is working, it just wants you to know that the computer doesn't charge the iPad.
If something's not working, try resetting your iPad when not plugged in. This won't remove any data or settings on your device, it might remove a glitch you're experiencing. To reset, press and hold Home and Power button at the same time until the Apple logo appears, then release both and let the iPad power up on it's own.
Hope that helps.