First thing to rule out--time/date error from the battery going dead. Connect to WiFi--usually by going within range of a WiFi source that the iPad has connected to before so it will connect automatically. Hard reset to restart. (Power and home buttons for 10 seconds)
If not solved, then you'll have to erase the iPad and start over--all data will be lost. You can force the iPad to boot into recovery mode by doing a hard reset (as above) but this time leave the home button connected and the iPad connected via usb to the computer.
This will prompt iTunes to ask if you'd like to restore the iPad--i.e. erase and start over.
jessa