Question 3rd and 4th ram slots don't work in 2 different boards with different cpu's

May 11, 2019
I recently upgraded from an Asrock b250m and i5 7600k to an msi z390-a pro and a 9600k. Before i upgraded but old motherboard would not post and i assumed the board was broken so i ordered the new parts. After i had finished replacing the parts in my system i had the exact same issue where the system would not post. I messed around and with it a bit and found out that the system would post fine with one stick of ram in either the first or second slots but the third and fourth slots would not post. So im not sure if my ram is the issue here or not, ive tried the sticks that do work in the third and fourth slots but still no boot. I also tried swapping out power supplies and checked the cpu socket on the motherboard and there are no bent pins. Im not sure what the issue is here. I am using corsair 4 4gb sticks vengeance 2400mhz ram.