Memory channels 3 + 4 cause PC to not post

[Solorin344]

My PC recently shut down randomly, after which it was fine for an hour or two, before shutting down a second time and refusing to post whatsoever. After disassembling and reassembling everything, I managed to get it to post with no GPU and 1 stick of RAM. I put everything back where it was supposed to be but it once again didn't post, just a black screen with the 'EZ Debug LED' flashing next to DRAM/CPU.

 

After testing every RAM slot configuration, both sticks seem to work fine, and the PC will boot (currently typing on it) if slots 1 and/or 2 are being used, but any combination of slots 3 and/or 4 being used cause the aforementioned black screen and debug lights flashing.

 

Specs are:

i5 9600K

MSI Z390-A PRO

2x8GB Corsair Vengeance RGB PRO 3200 MHz

 

I'm really not even sure what to try, any input would be greatly appreciated! Cheers.

[Airdragonz]

Check your motherboard manual to confirm, but ram should typically be in slots 2 and 4 if you're running 2 sticks. 

[Solorin344]

10 minutes ago, Airdragonz said:

Check your motherboard manual to confirm, but ram should typically be in slots 2 and 4 if you're running 2 sticks. 

Yep, 2 + 4 are the priority slots so to speak, and it has been running fine like that for about a year, then a couple of nights ago it shuts down and now the system will only post if there are no sticks in slots 3 or 4 (currently using only 1 stick in slot 2).

[Airdragonz]

1 minute ago, Solorin344 said:

Yep, 2 + 4 are the priority slots so to speak, and it has been running fine like that for about a year, then a couple of nights ago it shuts down and now the system will only post if there are no sticks in slots 3 or 4 (currently using only 1 stick in slot 2).

Have you tried resetting CMOS and/or disabling XMP to see if it'll work with anything in slots 3 or 4?

[Solorin344]

12 minutes ago, Airdragonz said:

Have you tried resetting CMOS and/or disabling XMP to see if it'll work with anything in slots 3 or 4?

Took the battery out, had to use a flathead to short it, XMP is off, still no post with those slots filled.

[Solorin344]

Solved! A lot of the advice for this sort of problem was bent CPU pins, which pointed me in the right direction. There were small bits of debris on the motherboard pins, only very tiny bits in 2 places, but it seems that was enough to take 2 memory channels out! I used a very fine brush to clean the pins, and now all 4 slots work again. Best of luck to anyone who has this problem in the future!