Thinking out loud here: A catastrophic failure, such as a seized connecting rod bearing, would normally result in a thrown rod because the cam would continue to spin after the bearing froze and the rod, not being able to move freely, would break from the forces on it. I think you would see something similar if your main bearings froze while the engine was running....one part stops, the others keep moving, and something is going to give way.

I would look at the flywheel and starter to see if something isn't jammed up there.