One of the oldest troubleshooting tricks in the book is to reboot the computer. It's amazing how many times this will solve issues. Let's choose to shut down the computer rather than simply restarting it. Once your computer is completely powered down, let it sit there for a few seconds before powering it back up.
And while we are waiting for the computer to come back up, let's go ahead and do the same thing with the iPad.
You can reboot the iPad by holding down the suspend button on the upper right hand corner of the device. After several seconds, a red button with an arrow will appear, instructing you to slide it to power off the device. Once the screen goes completely black, wait a few seconds and hold the suspend button down again. Apple's logo will appear in the middle of the screen while the iPad boots back up.
Once your computer and the iPad have been rebooted, try connecting the iPad to iTunes again. This will usually solve the problem.