[SOLVED] New system won't post, feels like I've tried everything (Z390m Pro4/9600k)

[DoctorThoss]

Hi all, I'm trying to troubleshoot a new build that won't post; never had an issue like this before. The system won't post, can't get anything to come up on screen at all, whether the monitor is plugged into the GPU or the motherboard. No beep codes to go by as this mobo doesn't have an integrated speaker and didn't come with one in the box. I've ordered a mobo speaker but it won't arrive for a while so I'm hoping it won't be necessary, but obviously I'll update with the beep code (if there is any) once the speaker arrives.
Here's what happens when the machine is powered on: everything with lights on it lights up (RGB ram, GPU), fans spin, and things look normal except for the fact that there's no output on the monitor. 20-30 seconds after boot, the system appears to restart; everything (lights, fans) turns off for about 5 seconds, and then everything comes back on. It only does this once. It doesn't loop or restart again, only once each time the system is powered on. When the system is turned off, it says off. I'm having trouble finding similar reports online so I'm hoping this is familiar to someone here; most of the issues I find online are people whose systems are restarting over and over, not just once.

Here's what I've tried already:

1. Removing GPU and connecting monitor directly to mobo
2. Booting with only 2 sticks of RAM
3. Booting with only 1 stick of RAM (tried each combination of the 4 sticks and the 4 slots)
4. Clearing CMOS
5. Double and triple-checked all cable connections to and from PSU

I've tried everything on the "try this first" page except for the system speaker because I don't have one yet as I mentioned above.

Does this issue sound familiar to anyone, or is there any other troubleshooting steps I can take? I know it's possible that one or more of my components is DOA, but I'm not sure how to narrow that down. Thanks so much in advance. Specs are below.

Mobo: ASRock Z390m Pro4
CPU: i5-9600k (not the KF model with no iGPU)
GPU: EVGA GTX 1070
Memory: GSkil Trident Z DDR4-3200 (4 x 8GB sticks for 32GB total)
PSU: EVGA G5 SuperNova 650W

 

[DoctorThoss]

I've seen reports that one potential issue is the question of whether or not my processor has P0 or R0 stepping, which is apparently impossible to determine by looking at the CPU or packaging itself (at least not anywhere I can see).

If this is the problem, I'm not sure what to do... the only other CPU I have here is an i7-4770k, which I believe won't work at all on the Z390m Pro4, so I can't use that as a control group, and I can't afford to purchase another CPU just to update a bios. I guess the move here, if it turns out this is the problem I'm having, is to return the mobo and buy one that is compatible out of the box with both stepping types?

Still I'm not convinced that this is what's happening so please let me know if you have other suggestions

 

[Vic 40]

No bent pins in the socket?

With that ram, and you already tried stuff, did you do a clear cmos and after that tested with just one stick in the second slot from the cpu out? Is A2.

 

[DoctorThoss]

No bent pins in the socket?

With that ram, and you already tried stuff, did you do a clear cmos and after that tested with just one stick in the second slot from the cpu out? Is A2.

Hi, no bent pins. And yep we cleared CMOS and tested with one stick in each slot, A2 first.

 

[Vic 40]

Most likely is that cpu or mobo is doa, can return both, see which one wil be replaced. Usually would i say mobo, but might wel be cpu seeing what troubles you have. Maybe start with that one.

 

[DoctorThoss]

update: tried booting with minimum components (cpu, psu, ram, cpu cooler) only on a test bench; same problem. Machine powers on, 30 seconds later it restarts, then stays on, but we never get any output to the monitor.

also confirmed via bios sticker that the bios version is 4.20; the p0/r0 stepping thing would only be an issue if version was below 4.0 so that ain't it.

If i'm going to RMA CPU and mobo, should I do ram as well in case that is the problem?

 

[Vic 40]

If i'm going to RMA CPU and mobo, should I do ram as well in case that is the problem?

That is up to you, might be good. Personally do i think either motherboard or cpu since even a single stick wouldn't boot.

 

[DoctorThoss]

update: all good! well, sort of. my brother had a spare z390 motherboard he let me borrow. With all the same components on his motherboard, the machine posted normally with no issues, and the CPU and all 4 sticks of RAM are detected properly. so it was my mobo that's no good, will RMA it. Thanks so much for all the responses.