If "Find my iPad" was enabled in Settings - iCloud, you have to remove your device there. First, turn off your iPad. Then access iCloud (icloud.com) on a computer and remove your device from "Find my iPad".
Here's how to do it: http://support.apple.com/kb/PH2702
Then restore the iPad: http://support.apple.com/kb/ht1414
If you have a backup without the passcode, then you can use it to set up your device. Otherwise you'll have to set it up as new.