Ashwith:
I meant that I connected a 12V lead acid battery to the DC plug. I touched the positive terminal to the ground over there. Saw a few sparks at the connecting wire and the board stopped powering up through the DC plug.
My guess is the diode or the voltage regulator.
Check the diode using an ohm meter. It should have very high or infinite resistance in one direction and almost no resistance in the other direction.