Question (SOLVED) New system will only post if ONLY the motherboard and CPU is plugged into the power supply.

[uponthenose]

Hello All,

I'm a veteran builder but this problem has me completely stumped. This is a ground-up, new build, my components list is below. After assembling the PC, there was no POST, no fans no clicks, the only sign of life was the CMOS, and SMART buttons were lit on the back of the MB. I went through the usual steps of removing components one at a time until finally I only had the motherboard and CPU, but still nothing was working. I removed the MB and tried it on the bench, jumping the power pins, but no luck. The PSU is brand new but I swapped it out with an older one I knew was working, no change. I assumed the MB was dead and RMA'd it with MSI who tested and returned it as fine. I replaced the PSU with a new one. I plugged the MB and CPU into the new PSU and again the CMOS and Smart buttons lit but nothing happened. I unplugged the CPU cables and wonder of wonders the motherboard went through POST far enough to recognize there was no CPU and then stopped. I then shut it down and plugged in the CPU cables and it again went through POST. My CPU cooler was not plugged in so after a moment the CPU began to get hot and I shut it down. I then plugged in the pump and again the system went through POST and stopped at no storage device. I plugged in the drives to the PSU and nothing happened. Only the CMOS and Smart buttons are lit, nothing else happens. Resetting the CMOS and tried again, but nothing happened. From that point on, nothing I do changes anything. If I leave only the MB, CPU, and pump plugged into the PSU it will boot to BIOS. If I add anything else at all to the PSU, nothing happens. I have tried three different PSU's all of them are of more than enough wattage for this system, all of them are listed as compatible with this MB by MSI the issue is the same. I have tried the MB on the bench and in the case properly screwed into the standoffs and that doesn't have an effect. My house is old so I thought maybe resistance in the outlet wires was causing a voltage drop, so I tried different outlets but had the same result. I also tried isolating the system from the outlets by plugging it into a UPS with a battery back up and the issue persists. Any help or ideas you can give me would be much appreciated!!

Here are my system components:
MSI z790 Carbon WiFi
Intel i9 13900K
Corsair Dominator DDR5 6600 MHz
GE Force RTX 3090 (installed on MB but not plugged in to PSU)
Hyper M.2x16 Card with 4x2TB M.2 drives
Corsair H150i cooler
6 case fans plugged into Corsair controller
Inwin Case
Corsair HX1500i and Thermaltake 1200W power supplies
Using series 4 power cables.

 

[Lutfij]

Corsair HX1500i and Thermaltake 1200W power supplies
The two PSU's are not from the same OEM, you should use cables that came with their units, respectively, not interchangeably.
+
Thermaltake 1200W
Thermaltake is the brand of the unit, what is the model of the unit?

GE Force RTX 3090 (installed on MB but not plugged in to PSU)
Without the discrete GPU you should get display output from the iGPU on that K suffix processor though why is it not pugged into the PSU while it was populating a PCIe slot on the motherboard?

Corsair Dominator DDR5 6600 MHz
This is vague, how many sticks of ram are you working with? If two, they should be in slots A2 and B2.

Corsair H150i cooler
Relieve some stress on the CPU's socket, cooling mount/block and see if that helps.

Breadboard the system and see if the system fires up with display.

Lastly, might want to add spaces in your wall of text to form paragraphs to aid in thread comprehension.

 

[uponthenose]

Corsair HX1500i and Thermaltake 1200W power supplies
The two PSU's are not from the same OEM, you should use cables that with their units, respectively, not interchangeably.
+
Thermaltake 1200W
Thermaltake is the brand of the unit, what is the model of the unit?

GE Force RTX 3090 (installed on MB but not plugged in to PSU)
Without the discrete GPU you should get display output from the iGPU on that K suffix processor though why is it not pugged into the PSU while it was populating a PCIe slot on the motherboard?

Corsair Dominator DDR5 6600 MHz
This is vague, how many sticks of ram are you working with? If two, they should be in slots A2 and B2.

Corsair H150i cooler
Relieve some stress on the CPU's socket, cooling mount/block and see if that helps.

Breadboard the system and see if the system fires up with display.

Lastly, might want to add spaces in your wall of text to form paragraphs to aid in thread comprehension.

LOL, thanks for the advice. I actually just solved my own problem. The SATA power cable I was using is not a Corsair cable. apparently, that's a big deal. I swapped that power cable for one from the Corsair bag and the problem went away.

 

[Lutfij]

You might want to consider yourself lucky that you didn't fry anything in the process using the wrong cable on the wrong PSU.