If I am reading you correctly, you had the board on a flat surface... a reinforced cardboard box, when you put the ram into it and heard something that sounded like the MB breaking.
Most likely it was the cardboard box. Motherboards are laminated and four to six layers thick. They don’t break or crack easily.
Add the CPU and the GPU and power the system while out of the case. If you can get to Bios and everything seems functional your good to go. Otherwise RMA the board.