iPad 2 won't open, just apple with bite on screen no boot up after 12 hours

I was previously cleaning up my email, turned off the iPad and when I returned later to finish my mail, I received the screen thar has iCloud, Yahoo, Google, Aol, and several others upon pushing the "mail" button. When I picked AOL, it asked for my email address and password, which I thought was odd, since I had always been able to open my email without signing in. The others all required signing in. I then thought that I would reboot the iPad by pushing the Home button and the on/off button together as I had done numerous other times when I had a problem. This time, pushing the buttons yielded the white Apple logo with a bite out of the Apple. I hooked it up to the charger, believing that it would reboot within the hour. Nothing happened after 12 hours. I was able to hold the two buttons done long enought for the unit screen to go black (assuming it was turned off). Before the problem above occured, I did have a little blue box show up indicationg I had a carrier update. I can't recall the screen I was on at the time. I don't have an active data contract with AT&T. My iPad 2 is 64GB model with about 2.5 GB capacity remaining.