How come my engine doesn't turn?

i hope you made sure you had it on tdc and timed correctly before you tried to start it the first time. and with the loud noise, its very possible you bent a valve. take your valve cover gasket off and inspect your rockers, make sure none of them are stuck. and what exactly do you mean by the pistons move in all directions? they all move up and down, but at different times. you probably should have checked into this before you tore into it, but get a book and check the tdc with the timing, and make sure you have your firing order correct on the distributor and the plugs on the motor.