Try first using a different USB cable, then the different USB port on the same computer, then a different computer if needed.
You can also try to put the iPad into DFU mode and see if iTunes recognizes it. DFU mode requires correct timing. To enter DFU:
1. Plug the iPad into the computer. On or off does not matter.
2. Begin holding both the power button and home button at the same time.
3. Once you have been holding both buttons for 9-10 seconds, release the power button but continue to hold home.
4. The iPad's screen should already be blank and your iPad should connect within a few seconds. You can let go of the button as soon as your computer notifies you something is detected.
If the screen lights back up, you have failed to enter DFU. You can try again as many times as needed.