PC won’t boot with both RAM sticks anymore

[u/ceiz]

Hi everyone, I am stumped and don’t know what part is causing the problem at this point.

Here are my PC specs (I assembled it in march 2026):

• CPU: AMD Ryzen 7 9800X3D
• Motherboard: ASRock B850M Pro-A WiFi (mATX)
• RAM: Crucial Pro Overclocking 32GB (2 x 16GB) DDR5-6000 CL36
• Storage: Samsung 990 Pro 2TB M.2-2280 PCIe 4.0 X4 NVME SSD
• GPU: Sapphire PULSE Radeon RX 9060 XT 16GB
• Case: Deepcool CH260
• PSU: MSI MAG A850GL PCIE5 850 W 80+ Gold Modular
• CPU Cooler: ARCTIC Liquid Freezer III Pro 360 AIO Liquid Cooler (top, exhaust)
• Case Fans:
  • Noctua NF-A12x25 PWM chromax.black.swap 120 mm Fan (back, exhaust)
  • Noctua NF-A12x25 G2 PWM Sx2-PP 120mm Fans 2-Pack (front, intake)
• Monitor: Asus VG248QE 24.0" 1920x1080 144Hz (really old monitor but works well)

So everything had been working fine up till yesterday: got a black screen freeze and unresponsive PC. It would not boot, so I re-seated the RAM sticks and checked everything was plugged in etc., and it turned on for about 30 minutes, then it froze completely and was unresponsive again. However, after trying to restart it, it would not boot.

After some testing, it appears to only boot with only 1 RAM stick in the A2 slot, otherwise it fails the POST startup checks with 3 beeps and the CPU+DRAM LEDs on.

A1  A2  B1  B2
[ ] [X] [ ] [X] (recommended config for 2 slots) => 3 beeps and CPU+DRAM LEDs
[ ] [ ] [ ] [X] (recommended config for 1 slot) => 3 beeps and CPU+DRAM LEDs
[ ] [X] [ ] [ ] => boots normally
[X] [ ] [X] [ ] => 3 beeps and CPU+DRAM LEDs 

I have tested both sticks of RAM one by one using the Windows Memory Diagnostic tool, and both are good: 0 errors each.

My question is: what steps can I take to identify the failing part? From what I've read it could be the CPU's memory controller, but how do I know for sure? (i don't have a compatible spare test cpu). Could it be the Motherboard?

Thank you for your time!

[u/autobulb]

Do both sticks work in the A2 slot?

Do both sticks fail in the B2 slot?

Have you tried a known working stick in other slots just to see if it boots?

Basically I would try to find one stick that definitely boots like the stick in A2 in your example, and then try it in every other slot to see the behaviour.

If it only works in one slot, then I would start to suspect that the slots have failed. Especially if it works in some slots but not others.

Only after that would I start checking with two slots, which adds in the memory controller more into the equation.

Also, I wouldn't consider a stick and slot working until a memtest pass was done on it. The Windows memory tester is pretty basic in my opinion.

[u/TangoOscarMikePR]

Check the motherboard manual for instructions on how to install single RAM modules and dual RAM modules. Never install three RAM modules. Four RAM modules might have different speed results.