iMac 2019, 27” 3.1 GHz Core i5 not booting mac OS

Well, some updates.

I contacted local assistance that would charge just to inspect. That is the plan F at the moment. Last resort only.

I left the Mac off for some 2 days, disconnected from the AC Power.

Now it passed the first screen on the installer, I could get until disk utility.

I even got to try to install it, next next and then, reboot again

I wouldn't suspect of RAM but I tried, just in case.

I removed the 2x8GB Crucial and tried to boot from my OS drive and it booted without a problem.

Well, it kept saying the nagging "hardwre problem" that I could just clicked ignore, just after logging in.

So kudos to your instinct! Thenk you for your ideas and help regarding this.

So I made the Etrecheck test that I share here.

While my mac was down, I connected the external drive (where my OS resides) to another mac, and I found some odd things.

A small partition saying update.

I tried in that mac first aid is disk utility (at this time I though it wouldn't boot because a corrupted disk) and it just gave an error, couldn't repair.

Fast forwarding to today, just after loggin in, I tried the first aid repair, same problem, something about the hard drive.

It says to repair in recovery mode.

I assume it is refering to rebooting with CMD+R and recovery from the internet.

Woudl that be differente of reinstalling ovfer the operative system, on top of my OS drive?

I already done that in the past.

The system is working ATM, but can have some kind of system corrupted files that I want to heal right now.

What would be the better way of healing the filesystem, without deleting everything and startin over?

-Receovery mode? (please confirm if I am thinkng OK, would be booting of CMD+R)

-Reinstalling over the OS drive, as I have done in the past, without losing data.

-Other option?

Regarding to the RAM, I am still not sure if the problems are with the sticks or with the slots.

I am saying this because the first KIT I bought, had two slots and when I booted with two, the mac wouldn't boot (I don't remmeber the problem).

I got to unterstand that one of the two was corrupted.

I sent it to RMA and got a new kit.

But I cannot ignore that the problem might be in the slot and not in the sticks.

So I will try combinations of dimms and run REMBER to see if I can catch the problems.

If I can boot memtest86 in UEFI mode (I only tried with the BIOS mode version and coudln't boot), I will try that as it seems to me more scientific.

Can you please clarify how should I proceed in order to deal with the filesystem problem?

Thank you!

I may check on that, but it is since 2019 working.

And if it was a ram problem, probably wouldn't pass the apple logo, even the installer shouldn't boot.

I think they are 4+4+8+8GB from what I remember.

Besides memtest86 I know, what could you suggest to see if it is memory problem?

Shouldn't the apple diagnostics see that?

Would the verbose mode help?

Thank you.

I will try the suggestion about the RAM, despite not being inclined to that.

That is because it was working without this kind of problem and windows boots just time.

And apple diagnostics suggests nothing about the ram.

But I will try to boot the installer without the RAM to see what happens.

In the meantime, this is the info of the RAM installed after the factory 4+4GB

I added this kit:

Crucial RAM 16GB (2x8GB) DDR4 2666MHz CL19 Kit de Memoria Mac CT2K8G4S266M

Crucial CT2K8G4S266M Kit de Memoria para Mac de 16 GB (8 GB x 2) (DDR4, 2666 MT/s, PC4-21300, CL19, Single Rank x 8, SODIMM, 260-Pines)

Will report back, thank you.

Why the copy paste of Old Toad's post?

And I already wrote it is a Crucial product...