How to Fix a Frozen iPad

Occasionally your Apple iPad may freeze or hang during an operation - some would call this a crash - and won't respond to the Home button, Sleep/wake button or the touchscreen.

If this happens there are two solutions you should try first:

Restart the iPad: press and hold down the sleep/wake on the front of the iPad for few seconds until the red slider appears, slide this across to shut the iPad down. Restart the iPad by pressing the Sleep/wake button on the top until the Apple logo appears
Reset the iPad: if restarting the iPad didn't work then you will need to reset the iPad. You can do this by pressing the Home button and the Sleep/wake button on the top the iPad's case and holding them down together for 10 seconds. The iPad should then reset itself
Restore the iPad

If neither of these two options fixes your unresponsive iPad then you will need to restore the iPad to its factory settings.

First make sure you have a USB 2.0 connection cable and the latest version of iTunes installed
Connect the iPad to your Mac or PC and launch iTunes
In the Devices section click on the iPad icon then the Summary tab and then click on the Restore button
When prompted, click on Back Up to back up all your iPad's media and settings
Then click on the Restore button
This will restore your iPad to its factory settings and install the latest version of the iPad operating software. Once this is completed, the iPad will restart
You can now restore all your iPad's media and settings from the most recent back up then click Continue. Your iPad should now be up and running again...

Source : http://www.knowyourmobile.com/appleiphone/ipad/ipaduserguides/458098/how_to_fix_a_frozen_ipad.html