Kernel Panic Loop At Boot & With Bootable Installer

Hi everyone. I was hoping to get some suggestions as to what could have gone wrong with my late 2013 iMac (model identifier 14,2) and find potential solutions. Friday morning I woke my iMac from sleep and was immediately greeted with a kernel panic. At that point it had probably been asleep for a week and a half without use.

Every time I turn on/restart the computer it will kernel panic. If I let it kernel panic in a loop enough times I will eventually see a prohibitory symbol (the circle with a slash through it). I have not been able to get past a kernel panic or a hung loading screen (from trying to boot it up in other modes) a single time over the past few days.

I have tried:

• Booting the computer with no peripherals attached (including a mouse and keyboard).
• Resetting the SMC.
• Resetting the NVRAM/PRAM.
• Running the Apple Diagnostics test. I’ve run it four times and it always finishes with no issues found (code ADP000).
• Trying to boot by cycling through all my RAM per stick and per slot.

I have also tried booting into: 1) safe mode, 2) recovery mode, and 3) internet recovery mode. I have not gotten a kernel panic when attempting to use those modes but all hang up on the screen with an Apple logo and a progress bar and will not complete. Internet recovery does let me select a network but hangs afterward. I have let the computer sit on those screens for over 2 hours without any progress.

I have tried booting into verbose mode but it also kernel panics. I have booted into single-user mode without a problem but am not able to do anything in it. That mode is well beyond my expertise anyway.

Finally, I have tried to use a bootable installer with macOS Catalina on it. I have successfully used this drive to reinstall macOS within the past 6 months. I get an immediate kernel panic when I select the drive to boot with. I am not able to access Disk Utility to check any drives for errors because of this.

I don’t think I’ve installed any new software or updates within the past month. But it doesn’t seem like a software issue if I can’t even boot off a USB drive. That is what is throwing me through a loop.

To be transparent, about 6 months ago I disassembled the machine to address persistently high temperatures (due to extremely compacted dust in the chin) and to install an SSD in place of the hard drive. It originally came with a fusion drive, so there’s a blade SSD installed on the logic board that I didn’t physically touch where the OS is installed. I also did not touch the CPU or remove the heatsink from the logic board. It has worked great for the last 6 months. The machine has not been moved off my desk since then.

I’m out of ideas of what I can do short of cutting off the screen again. And what would I even look for beyond the hard drive seating? While I am confident the drive cables were secure, could a loose cable on a secondary drive cause all these issues? Could a dead PRAM battery be responsible? What are the odds that all my RAM went bad at the same time?

I called Apple Support to inquire about getting it serviced but because this model iMac is over 8 years old it is now on the vintage list, so they might not be able to repair it if I take it in.

Thanks for whatever insight you may be able to help with!