thrown rods

okay, when i brought my 91 toyota corolla i started it up and there was loud banging noises. So then i took off the oil pan and i saw the ends of the connecting rods broken. I want to know, what would made the car do this and would i have to take the heads off to see about the pistons. Also, since im in there, what could i do to prevent this from happening again. Thanks!!

Also, would i have to take out the pistons to fix this problem?

never done any major engine work myself, but i'd probably go in from the bottom and pull the crank and pistons and see how the drivetrain works. might not be a bad idea to pull the head and see how that looks, though