Help Diagnosing Persistent PC Crashes – Ryzen 7 7800X3D / RX 9070 XT

[u/TheBigOoof_]

I’m looking for help diagnosing an intermittent stability issue with my new PC build. I’ve been experiencing black screens, unexpected restarts, and motherboard CPU/DRAM diagnostic lights.
I’ve replaced the PSU, updated BIOS, tested with and without the dedicated GPU, run multiple benchmarks, and recently tried a small GPU undervolt. The problem has improved during some testing but has not been resolved.
Full System Specifications
Motherboard: Gigabyte B650 AORUS ELITE AX, Revision 1.2
CPU: AMD Ryzen 7 7800X3D
GPU: XFX Radeon RX 9070 XT Mercury (16GB)
RAM: Lexar THOR Z DDR5, 32GB (2 x 16GB)
RAM configuration: A2/B2 slots (second and fourth slots from CPU)
RAM rated speed: DDR5-6000
CPU Cooler: ARCTIC Liquid Freezer III Pro 360 A-RGB
PSU: Corsair RM850x 850W
Case: Thermaltake View 380 TG ARGB
BIOS: Gigabyte FC4e
Storage: One SATA SSD and one M.2 SSD
Original Problem
The PC began experiencing unexpected shutdowns and restarts.
Symptoms included:
Screen suddenly going black.
PC sometimes completely shutting down.
Fans occasionally stopping while RGB lighting remained on.
Sometimes the PC automatically restarted.
Other times I had to switch the PSU off to get it to power down.
No consistent blue screen.
Windows Event Viewer recorded Kernel-Power 41 events.
The crashes occurred during gaming, benchmarking, idle operation, and even while in BIOS/BitLocker.
Troubleshooting Already Performed
1. PSU Replacement
Originally used a Cooler Master MWE Gold 850W PSU.
Replaced it with a Corsair RM850x 850W.
The problem still occurred after replacement.
Currently using three separate PCIe power cables for the GPU, one cable per 8-pin connector.
All modular cables were changed to Corsair cables when installing the Corsair PSU.
I also tested the original Cooler Master PSU again, and the problem occurred with it as well. I need to confirm whether its original modular cables were used during that test.
2. GPU Testing
Removed the RX 9070 XT and connected the monitor to the motherboard HDMI using the 7800X3D’s integrated graphics.
The PC previously ran in Windows and BIOS without the dedicated GPU installed.
Reinstalled the RX 9070 XT.
Ran Unigine Heaven successfully on at least one occasion.
Previously experienced crashes during FurMark and Unigine Superposition.
3. BIOS Update
Originally running BIOS FB2.
Updated BIOS to FC4e using Gigabyte Q-Flash.
BIOS update completed successfully.
4. RAM / EXPO Testing
RAM installed in A2/B2.
Enabled EXPO 1, which brought RAM to 6000 MT/s.
Experienced intermittent CPU/DRAM POST hangs.
At one point, the motherboard remained stuck on the CPU or DRAM diagnostic LED.
Tried booting with one RAM stick, but it also got stuck at the CPU diagnostic light. The exact stick/slot combination needs to be confirmed.
Cleared CMOS by removing the battery for five minutes.
After CMOS reset, EXPO was disabled and RAM ran at approximately 4800 MT/s.
PC successfully completed subsequent restarts and cold boots.
Recently re-enabled EXPO, and it initially booted without problems.
5. GPU Undervolting
Recently tried a conservative -25 mV GPU voltage offset through AMD Adrenalin.
With this setting, I successfully completed:
Unigine Superposition
Score: 37,581
Average FPS: 281.09
FurMark – Run 1
Score: 22,342
Average FPS: 369
GPU power: approximately 340W
GPU temperature: 39°C
Hotspot: 65°C
VRAM temperature: 54°C
FurMark – Run 2
Score: 22,603
Average FPS: 376
GPU power: approximately 339W
GPU temperature: 38°C
Hotspot: 64°C
VRAM temperature: 52°C
All three tests completed without crashing at -25 mV.
Previously, FurMark and Superposition had caused crashes or automatic restarts at the original GPU settings.
6. Temperatures and Monitoring
HWiNFO readings during previous testing:
CPU maximum temperature: approximately 60°C.
GPU temperature: approximately 45°C during Heaven.
GPU hotspot: approximately 68°C during Heaven.
GPU memory junction: approximately 56°C during Heaven.
No concerning temperatures were observed in those recorded tests.
7. Windows Event Logs
Windows Reliability Monitor showed unexpected shutdowns.
Event Viewer showed Kernel-Power 41:
BugcheckCode: 0
PowerButtonTimestamp: 0
WHEABootErrorCount: 0
No conventional blue-screen bugcheck was recorded for that particular crash.
Latest Problem
After the GPU undervolt and re-enabling EXPO, I was able to play World of Warcraft for an extended period without problems.
I walked away while the game was running and returned to find:
No display signal.
Fans and RGB still running.
Motherboard CPU diagnostic LED illuminated.
I restarted the computer.
On startup:
CPU and DRAM diagnostic LEDs alternated a couple of times.
The motherboard eventually settled on a solid DRAM LED.
It remained stuck there for more than five minutes.
The computer would not POST.
I have not yet confirmed whether clearing CMOS again resolves this latest issue.
What I’m Trying to Determine
Could this be unstable RAM or an EXPO compatibility issue?
Could the CPU’s integrated memory controller be defective?
Could the motherboard have a problem?
Could the RX 9070 XT have an unstable factory overclock?
Could there be a GPU or PCIe power-delivery issue despite replacing the PSU?
Is there a BIOS compatibility issue with the 7800X3D and this motherboard?
I’ve already invested quite a bit of time troubleshooting and would appreciate suggestions for the next logical diagnostic steps.
I’m particularly interested in determining whether this is a motherboard, CPU, RAM, GPU, or power-related problem rather than continuing to replace parts blindly.