If you haven’t already, be sure to check your power source. We’ve already said that it’s likely you can’t charge your iPad using a computer’s USB port, but if that has worked for you in the past and isn’t working now, make sure the computer is fully awake (not in sleep or hibernation mode).
You can also try a different USB port, in case the USB port you were using has failed. Don’t try charging from a USB port built into a keyboard or USB hub – connect it directly to a USB port on the computer itself.
Your best bet, though, is to plug the iPad directly into a wall outlet with an AC adapter. If you have been using an AC adapter this entire time, then try a different one — borrow one from a friend or try the one that came with a different USB-powered device. And of course, if the outlet is “switched,” be sure the switch is turned on so electricity is flowing to the outlet.