You have to use recovery mode if you want to unlock it and you will lose everything on your iPad if you do this. You can download your content again as long as you use the same Apple ID, but that will take some time, I'm sure.
Recovery Mode Instructions
- 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.