Overheating and not turning on

I have an Arduino Uno with a seeed motor shield, a ping sensor, and 8 AA batteries on it. It was working until 15 minutes ago, when It was driving around, it all of a sudden got reaaaaaalllllllly hot then I unplugged it and let it cool down, and now it won't turn back on. Please help me.

I also have all of the seeed output pins filled, but the two stepper ones, and I have a ping sensor hooked up at 5v gnd and 7.