If you have tried rebooting by holding both the power and home buttons until the apple logo appears has not worked, try it again but be sure to hold both buttons longer than usual, may take more than a minute to work.
If that still does not work, have you tried connecting to a computer with iTunes to see if iTunes recognizes the iPad? While this will erase the iPad, you may need to use the recovery mode to connect, per the instructions in http://support.apple.com/kb/HT1212
And if that does not work, it is time for a visit to the Apple store genius bar to have the techs check it out.