DDR4 Ram works with 2 sticks but not 4

I have a computer that worked a few days ago but I took it apart to install some extra fans. Now pc wont work with all 4 slots populated and only works with 1 or 2 sticks of ram. I've tested all 4 sticks on the board and they all work. Mobo is a asus prime b550m-a wifi 2 and ram is ddr4-2133mhz.