You probably need to use recovery mode now.
You can read about it here or follow the instructions below.
http://support.apple.com/kb/ht4097
- Disconnect the USB cable from the iPad, but leave the other end of the cable connected to your computer's USB port.
- Turn off iPad: Press and hold the Sleep/Wake button for a few seconds until the red slider appears, then slide the slider. Wait for iPad to turn off.
- If you cannot turn off iPad using the slider, press and hold the Sleep/Wake and Home buttons at the same time. When the iPad turns off, release the Sleep/Wake and Home buttons.
- While pressing and holding the Home button, reconnect the USB cable to iPad. When you reconnect the USB cable, iPad should power on.
- Continue holding the Home button until you see the "Connect to iTunes" screen. When this screen appears you can release the Home button.
- If necessary, open iTunes. You should see the recovery mode alert that iTunes has detected an iPad in recovery mode.
- Use iTunes to restore iPad.