I recently acquired a Packard Bell Executive Multi-Media (9003D) computer that had been sitting a garage for a couple decades. Aside from some tarnished screws, dead bugs and dust, it looks to be in fairly good condition. No caps are bulged, leaking (although that doesn't rule out them being dry), no obviously tarnished or dirty connectors, etc. I gave it a clean with some IPA anyway before turning it on. It came with two ISA cards, some modem/network card and sound blaster 16, and had all 4 SIMM slots populated, one bank being a mismatched pair of sticks (and the default CD-ROM, HDD and floppy reader).
At the time I didn't have a PS/2 keyboard or mouse to hand but I still wanted to check if would even turn on, which it did, and it booted into windows 95 successfully. As I was moving it around, I pressed what I now know is the Reset button on the front, and that took me back to the POST screen where I noticed a message telling me insert some bootable media. I'll be honest I didn't take much notice of the message at that point because I wasn't sure what the button I pressed did, so I kind of assumed that was normal.

Fast forward to where I have a suitable keyboard (which for context is just a raspberry pi translating USB to PS/2 for now) and I go to try and explore this computer only to encounter the bootable media error which I have since been unable to get past. I was noticing during POST it was listing "Floppy A" as "installed". There is a floppy reader but no floppy inside, so I'm not sure if that message meant it thought there was a ghost floppy in the reader, or just that there was a reader available. Either way, I started by replacing the CMOS battery as that was obviously dead, which meant I could save BIOS settings (and disable the floppy) but that didn't change the symptom described earlier.
While in the BIOS I spotted the real symptom which was that both the primary and secondary IDE positions were listed as not installed, which is not true because the internal HDD is connected to the primary IDE header, and the CD-ROM is connected to the secondary header (I tried swapping them with no change). Both also have their jumpers set to the master position. I reseated everything but still none were registered. Up until this point I considered the possibility the HDD was dead, but even if that was true I would still expect to see the CD-ROM, as they both are in separate slots and do not share a cable.
I tried a few different things, like changing the HDDs jumper position to all available positions, removing the mismatched RAM, expansion cards, and even disconnecting the HDD entirely, but I was having some inconsistent POSTs with inconsistent error beeps. I commonly had one short beep, which I think means DRAM refresh error, but I also had 2 short beeps, 3 short beeps, and even 3 long beeps which I couldn't find docs on. There is a caveat here where I think my monitor was not consistently being woken up if the computer did POST, so I can't be certain all were failures. I also did a check of PSU voltage rails, which all came back clean and consistent, including the Power Good signal which had a clean and fast transition from 0V to 5V.

Since then, I have still been unsuccessful in getting either IDE device to be detected. This is making me think somehow the IDE controller IC (Intel PCIset SB82371FB) has died. I hope this isn't the case, and I'm not sure how a single reset could've killed it, but I'm out of other ideas.

Does anyone else have any ideas of things I could check?