Put your iPad in DFU mode and then do a restore.
1) Plug iPad into mac with USB cable
2) Power off the iPad
3) Hold Power button for 3 seconds
4) Keep holding Power button and also press home button, hold for 10 seconds
5) Keep holding Home button and let go of power, hold another 10 seconds
iTunes should then show your iPad is in recovery mode. The screen of the iPad should be black. If you see the picture of the cable and iTunes you are in recovery mode not DFU.