Restart and or reset the iPad:
Restart: Hold down the power button until the power off slider appears. Slide it off. When the iPad finishes shutting down, hold down the power button again until the Apple logo appears.
Reset: Hold down the power and home buttons until the Apple logo appears. The iPad will reboot. This usually takes a bit longer than a restart.
Restart the computer.
Try a different USB port on the computer.
If you have spare iPad cable, try that.
Reinstall iTunes.
And if all else fails, give Apple a call.
That's all I can think of at the moment.