Hello there! I'm having some problems breathing life back into my dad's old computer.
I have a little experience with building a computer and fiddling with the bios, but most of that is limited to my 2019 build, so I'm running into a few walls trying to get this computer running again.
Here's what I do know:

-The computer starts. The power SUPPLY is fine, the fans all work, and there's enough RAM to prevent immediate crashing.
-It doesn't boot. There's either a PROBLEM with the hard DRIVES, or a problem with the software, or a connection issue with the hardware. I've made sure all the connections (that I can see) are correctly seated, but there might be some missing cables I don't know about.

I don't know much about the actual guts of the computer. I know it has one RAM card right now, and two hard drives, but I'm unsure if those are still useable or not. It sounds like they spin up, so hopefully they are still okay. It also has two CD-ROMs and one floppy disk drive. I believe the motherboard is from MSI (its the company logo that shows up on START).
I'm also not sure about that OS it's running. I suspect it's Windows 98, but this is only a guess.
I've booted it up a couple of times, trying a few different routes to get it to work. The first time, I just let it run on its own until it encountered an error:

PXE-E61: Media test failure, check cable
PXE-M0F: Exiting Intel PXE ROM

Boot failure from previous device..

Boot failure
Insert BOOT diskette in A:
Press any key when ready

The second time, I tried to get into the bios, but I wasn't able to. I pressed Tab instead to enter POST (which I don't know what that is) and it began auto-checking for primary and secondary masters and slaves. It found none, and the screen promptly went black.
I'm guessing there's either a software issue, one that will require me to dig through the plethora of floppy disks that are hiding in the basement and hope that I can find the one which allows me to successfully reboot the computer, or there's a hardware problem which I haven't been able to diagnose.
I'm hoping someone here might be able to give me a little direction so I can get this beautiful dinosaur on its feet again ^^
Edit: after some testing and actually touching the HDD's, it seems that they are not spinning up. Since the CD-ROMs are functioning (I put a disk in and they spun up fine) its not the power supply. Possibly a cable that needs replacing, or the hard drives have straight up died.
I have some spare ones lying around, but I'm not sure if they'll work in the old setup, and on top of that the floppy disk reader is non-functional as well, so I'd have to somehow pre-load Windows 98 or 95 onto it (I'm starting to think the original operating system was 95 based on the floppy disk I found).
Would this work? Are there some other workarounds that might work? I could use some ideasReplace the battery on the motherboard.