RESOLVED: ASUS Prime Z270 no-POST has me stumped

So I actually joined about a week ago because I find a lot of the other stuff, especially the home server stuff, exciting. But I’m in the middle of a couple budget builds and one is no-posting in a way that absolutely has me stumped. I was googling and actually got a result for this forum, so I thought, why not ask here. People seem less judgmental here than other places.

My experience: I’m not really a hardware guy, I have a BS in Computer Science, switched from IT but not until after I got a Network+ for fun, now about to graduate with an MS in Cybersecurity. I have built or upgraded a number of computers, and I’m the family “tech support” but I am far from having the type of experience many of y’all have.

The build is based around an i5-600K on a ASUS Prime Z270-A motherboard, along with 16GB Corsair Vengeance DDR4 3200 and a ROG Strix GTX 1060.

I had this build working previously, but I am building a very similar rig for my wife and during that process we were having trouble getting hers to boot. We discovered the issue was a suspect EPS cable that had come with one of our EVGA 650 PSUs (think it was her BQ but might have been off my GA). Either way, being the dedicated and loving husband that I am, it only took a little complaining on her part for me to sacrifice mine off my working rig and order myself a new one.

In the process, I did switch CPUs since mine was known to be working. Fast forward a week or two, wife is happily playing Fall Guys on her shiny new rig, kids are annoying us with Among Us and Minecraft, the new cable is here, and I’m rebuilding mine, but now it won’t post. I am absolutely stumped.

Here are the symptoms and steps I’ve taken:

Mobo RGB lights up when the PSU is turned on. When the mobo power button is hit, I get the red CPU light, it quickly turns off, the yellow DRAM light goes on then off, then…nothing. There is usually a VGA light but I am not seeing it light now, and I cannot recall if it goes with the onboard iGPU only or if it should always light up. I can’t seem to find a trustworthy answer on that. The RGB goes, including for the GPU. Cooler and GPU fans spin. RAM RGB goes. But no further lights, no boot single-beep or beep codes (I am old school and used a speaker), no display.

The motherboard manual indicates on ASUS boards, these lights should stay lit if an issue is detected with their associated components, so the motherboard seemingly does not see anything wrong.

-Tried removing the GPU and going with onboard. Same result.

-Tried going down to 1 stick of RAM, same result.

-Tried removing RAM, I get the no-RAM beep code.

-Swapped for a Celeron 3930 I have laying around that should be good, same result.

-Cleared CMOS between many of these steps.

-Tried more different RAM I had laying around (EVGA Superclocked DDR4 2400 and Patriot Viper 2400)

-Swapped display cables, nothing. Swapped from DP to HDMI, nothing.

-Tried a different monitor with both DP and HDMI, no joy.

-Tried going no CPU, wouldn’t even try to boot as much as before, no lights.

-Tried pulling the EPS cable entirely, also wouldn’t even try to boot like before.

-Tried doing the BIOS flashback feature using the specified port and a USB stick, nothing.

-Tried both the 6600K and the Celeron in another Prime Z270-A from eBay that showed up with a few bent pins so I did not initially use (it was supposed to be my wife’s board but she lucked out bc the guy refunded us but said keep the board, and we ended up getting an amazing price on a Z270 Maximus IX Hero)- did not expect this one to work, it was a hail mary.

All of these components were good and validated in this specific as-of perhaps two weeks ago when the PC was running. I checked the socket and I see maybe a couple sussy pins but nothing too scary- and again, it was working two weeks ago with essentially these exact parts.

I am led to the following conclusions:

1. if the EPS cable was bad (again), I would get the same no attempt to boot as I do when it is removed entirely.

2. The motherboard is suspect but must at least be somewhat okay given the no-RAM beep codes and general appearance of almost, but not quite, booting.

3. The CPU is unlikely to be the issue, which leaves the motherboard or PSU, but see above for the motherboard and the PSU was working as of last week (tried it on the wife’s build and it worked) so is unlikely to be the culprit.

For all the world I would say it was somehow booting but not displaying any video, except for the lack of a boot beep.

As I said above, I have some experience but not the most, and maybe I am missing something simple but this has me completely stumped. The only other thing I can really see to try is swapping in my wife’s CPU, and if the issue_is_ the slightly suspect socket pins, they got bent whilst I was swapping them troubleshooting her build, so I am loath to try again. I am 6’4″ with giant blunt sausage fingers (my friends call me Magilla Gorilla, hence the screenname), so LGA sockets in general give me the heebie jeebies and I try to avoid messing with them if at all possible. With my bad eyesight, I can barely even see the pins!

I am very sad because I just found this L1T forum guide to modding the bios of this motherboard because I suspect it will unlock ReBAR on my board and let me use the a770 I got for Xmas (shhh it’s s surprise, don’t tell anyone lol).

Thanks for reading this ramble. Any and all ideas welcome.

EDIT: Added a couple troubleshooting steps I had forgotten