Question New computer won't start with 8-pin EATX connected

Sep 27, 2021
Last week I decided to upgrade my 12 year old i7-2600k processor with a new one. The old one was starting to show it's age, and I felt justified bying a new upgrade seeing as I've had the old one for for more than a decade.

I bought a new motherboard, new RAM, a M2 SSD and a new CPU. Seeing as my graphics card is fairly new and my watercooler works fine, I decided to keep those and my old PSU.

I built the new PC got everything in the old cabinet and tried starting it up. When I started it up it wouldn't start up properly. It powers on for about 0.5 seconds, the fans, the water pump and the lights turn on, but instantly turn off and goes into a boot loop. Having experienced this before, my first thought was that it was some kind of short. When I built my first PC 20 years ago I had forgotten to put in the spacers in the cabinet and had the same problem. To see if that might be the problem I decided to breadboard.
I took everything out, put it on a cardboard box and started eliminating components.
In the end I was left with the CPU in it's socket, the CPU-fan and one stick of RAM. Everything else was disconnected. No matter what I did I only got the same bootloop.
Seeing as the CPU-fan and the PSU was (and is) working fine in my old computer, and that removing the CPU and trying to start with just one stick of RAM and the CPU-fan didn't resolve the problem, I concluded that it was the motherboard. Contacted the retailer I bought it from and got sent a new one.

Today I got the new motherboard. I tried assembling everything again, but instead of inserting it into the cabinet I started testing it while breadboarding. I installed the CPU in its socket, I fastened the CPU-fan and connected it, and I added one stick of RAM. Tried starting the computer and felt my heart sink as the same problem prevailed.
After getting the new card I did a thorough comparison of the old motherboard and the new motherboard and found that the old motherboard had one bent pin in the LGA Socket. That could explain why it didn't work with the previous motherboard, but the new motherboard had no bent pins, and I couldn't find any other issues with the motherboard either.
I've googled and tried every single variation of components connected and disconnected, I'm at my wits end.

As a last hail mary, I realized I hadn't tried starting the motherboard with the CPU power disconnected. I didn't really expect it to work, and even if it did work, it wouldn't really help me, but I decided to disconnect the 8-pin EATX cable from the motherboard. Lo and behold, it worked.
Seeing as it worked when the CPU wasn't powered I tried removing the CPU, reconnecting the 8-pin EATX and tried powering it on again. That didn't work, I was back to the old bootloop again. I've used the correct EATX cable, it's the 2x4 pin CPU cable, not the 2+6 pin GPU cable.

Does anyone have any ideas what it could be? Does anyone have any suggestions as to what I can try? I'm getting desperate and slightly pissed off that I'm unable to get this to work.
I guess it could be the PSU, but seeing as it works with the old computer that seems unlikely?

Motherboard: Asus TUF Gaming Z590 Plus
CPU: Intel Core i7-11700k
Memory: Corsair Vengeance 2x16GB 3200Mhz RAM
CPU-Fan: Corsair H60
PSU: Lian Li 850W Silent Force

TL:DR What I've tried:

  • Breadboarding with only CPU, CPU Fan and RAM connected -> Bootloop
  • Breadboarding with only CPU Fan and RAM connected -> Bootloop
  • Gotten a replacement motherboard -> Bootloop
  • Breadboarding with CPU, CPU Fan and RAM connected, and 8-pin CPU Power EATX cable disconnected -> Powers on, but it doesn't really help me get anywhere.
Sep 27, 2021
Yes, as it is, the PSU seems to be (and hopefully is) the main suspect. The PSU was bought a few years after I bought the CPU, but seeing as it was first manufactured in 2008 I guess it could be too old.
I will order a new one and report back if it fixes the issue. Thanks for the suggestion InvalidError.
Sep 27, 2021
If that PSU is nearly as old as your Sandy Bridge PC, then it is a pre-Haswell design that likely isn't capable of coping with modern CPU VRM transients. Lots of good-back-in-the-day PSUs don't make the Haswell cut.
I got a new PSU today and I still have the same problem. Tried starting it without the CPU installed, so I doubt the CPU is the problem. You’d think it at least would get to POST without the CPU. That only leaves the motherboard. But how likely is it that I’ve gotten two motherboards that are DOA? I’ve made sure I’ve grounded myself before handling the components, so I’m pretty sure that is not the problem.
I’m seriously considering just saying <Mod Edit> it and send everything back. The 2600k might be old, but at least I can get that one to work.
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Tried starting it without the CPU installed, so I doubt the CPU is the problem. You’d think it at least would get to POST without the CPU.
You cannot POST without a CPU since the CPU is the one running the power-on self-test code from BIOS which includes basic stuff like configuring the memory controller, initializing all of the basic peripheral controllers, performing a couple of basic tests, detecting the GPU if present, initialize the GPU so POST progress can be reported on-screen, etc. Likewise, "booting" with CPU-power missing won't work since the CPU gets no power to run through POST. The only reason the PC is staying on is because the CPU isn't there to tell the power-management chip "I'm <Mod Edit>, shut down now."

The only two times I've had a new PC fail to boot on the first try were both Ryzen motherboards that required BIOS update to address memory compatibility issues.

You could try resetting CMOS. Maybe it somehow ended up with garbage values it wasn't supposed to get and are preventing it from booting. Keep in mind that the system may boot loop for several seconds initially as the BIOS is iterating through memory controller parameters for memory controller training. When I put my i5-11400/B560 TUF together, the system reset 4-5 times on first power-on and another 2-3 times after each DRAM profile tweaking attempt.


How old is that Corsair H60? If its 5+ years old it may have permeated a huge portion of its water by now and the pump may be on its way out as well. How were the temps with the 2600k and the h60? Are you sure you are connecting the radiator fans to the CPU labeled fan connector on the motherboard? Have you checked the pads on the bottom of the 11700k? If, for some reason, one or more of the contacts are dirty or that can cause issues. Are you sure you connected the 20+4-pin connector and the 8pin CPU connector properly on the motherboard and PSU sides? 2 bad motherboards or 1 bad CPU? The odds are low in both cases but if one or the other happened my bet would be on the CPU. You definitely have an odd issue.