What's the model number of your Pentium 3 board?
And if might be easier if you added all relevant information here instead of just linking to another thread which contains masses of information, only to perhaps find out the model number hasn't been added there anyway.
It could be several things.

Assuming that this is an IDE/PATA drive- and without delving to deep into the thread you linked to....

Have you verified the ribbon connectors are installed correctly pin 1 to red? Some older drives, are picky about being the first drive on the cable. Have you verified that the jumper for master/slave is configured to match actual as used on the ribbon connector. Tried the drive in a different, known working system? Are you able to otherwise access the drive from the prompt? Is the drive the only device on the controller? All of this off the top of my head.

Boot from a floppy with CDROM drivers (like the boot floppy of Win98) and try to read the CD in question. I bet the drive won't read it.

At a pinch you can put the hard disk in another machine, create your C partition to install into, format and make bootable, create a second partition on the same disk and copy the OS CD into it. Put the drive back in the original machine, boot to dos prompt, and install from the second partition as if it were a CD drive. I'm sure I've installed Windows XP this way on a particularly awkward PC.

Sorry I forgot to add the mobo model: ASUS TUV4X
I connected the drive correctly and the same drive with the same ide cable is working perfectly on my other AMD Duron computer

CD boot enabled? Master/Slave jumpers set right?

Yes, everything is set up properly in the BIOS, I tried both with CD boot enabled and floppy boot disabled and with both enabled and then giving the priority to CD

I can't seem to find a key for the boot menu to choose what device boot from... usually it's F8 or F12, but none of them work on this motherboard apparently.

Long shot :
PSU's 12v rail is on its way out and prevents the drive from spinning up properly ?

The drive spins and works fine when I use it in the operative system on that P3 PC, it just doesn't let me boot from the CD-ROM drive for some reason, it just skips it and tries floppy and hardisk even if I put it on the first priority in the boot order in the BIOS.

boot PLOP bootmanager from Diskette and select CD-Drive.

Elia1995 wrote:

The drive spins and works fine when I use it in the operative system on that P3 PC, it just doesn't let me boot from the CD-ROM drive for some reason, it just skips it and tries floppy and hardisk even if I put it on the first priority in the boot order in the BIOS.

Do you see the "Booting from CDROM..." message/attempt before it eventually boots from the other devices?

No, I don't know if it appears because my TV refreshes during the boot and all I can see is either a missing drive error if there isn't an HDD connected, or directly the Windows 98 boot picture.

Having nothing connected, there should be a "Booting from CDROM..." + a "Failure" there when you get the picture back, before the error. I'd focus in BIOS settings and nothing else, since you're certain that this drive reads discs on this specific machine. I'm not even discussing trying any of the discs on another machine, I assume you've already done it.

Exactly, the drive works fine, even digital CD audio and with the audio cable that goes from the drive to the CT4750 works fine.
I've already installed a lot of games from disks on that computer and the drive works perfectly, I installed Windows 98SE on that hardisk from another computer but with the same exact drive, from which it booted just fine.

In the BIOS > BOOT tab I set the priorities as follows:

1st boot device: CD-ROM *model name and stuff*
2nd boot device: Legacy Floppy
3rd boot device: MAXTOR *model numbers*
4th boot device: Ethernet (put this as last because I've never even used it on any PC so far in my entire life)

There is no Failure or errors in the boot when the display starts showing stuff, I only see the Windows 98 logo and then the autoexec commands (when it loads CTMOUSE for the MS-DOS mode and the SET BLASTER parameters) followed by the desktop.

Good advice has been given in this thread 😀

In addition to what's already been said:
Have the TUV4X removed from any casing and place on a testbench. Have both a PCI and AGP card ready (you could just use the graphics card that's already working on this system), remove all harddrives and any other expansion cards like NICs and sound cards.
For now, don't bother with the optical drive you already tried, use one of your other systems (which should work since you tested basically all of them by now I think? 😜) and attach that to the primary IDE adapter on the motherboard. Iirc the VIA chipset of your board doesn't have onboard graphics.
If removing the board from a case, you might as well remove the BIOS battery and have it without BIOS battery for a day or so. But you may do the "remove battery for a day-trick" after having exhausted other options (btw I don't think this is likely the problem anyway, but it's very low effort so hence I brought it up).

Use the ribbon cable you used for your optical drive you used in the rig that you removed the optical drive from (so we know the ribbon cable should not be a problem here). Attach the optical drive to the primary IDE (forget about the secondary for now) and attach as master if you can. I typically don't bother with cable select or auto-select...whatever... with stuff this old.

And use another PSU, preferably one that is known to work (and the PSU from the rig the TUV4X is from will be designated as not known to work, since this might be the actual problem here! 😜).

The TUV4X case doesn't have any PSU, I just plugged in my usual testing ATX PSU to give it power.
And that is the only IDE CD/DVD-ROM drive I have, since there aren't any SATA ports on that board I can't even test in another optical drive.
I tried all the other optical drives I found in "the loot-box", but it seems they're all dead or got some problems:
some don't open at all, while some open but don't read any disk, so I'm stuck with this only 100% working IDE optical drive for all of those computers at the moment.
I then of course have some SATA ones, but I can't plug them into a board that doesn't have any SATA beginning with.

Elia1995 wrote:

The TUV4X case doesn't have any PSU, I just plugged in my usual testing ATX PSU to give it power. And that is the only IDE CD/DV […]
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The TUV4X case doesn't have any PSU, I just plugged in my usual testing ATX PSU to give it power.
And that is the only IDE CD/DVD-ROM drive I have, since there aren't any SATA ports on that board I can't even test in another optical drive.
I tried all the other optical drives I found in "the loot-box", but it seems they're all dead or got some problems:
some don't open at all, while some open but don't read any disk, so I'm stuck with this only 100% working IDE optical drive for all of those computers at the moment.
I then of course have some SATA ones, but I can't plug them into a board that doesn't have any SATA beginning with.

Only a single IDE optical drive? I'd say it's time for you to do some second hand shopping 😜
Where I live, IDE drives are still easy to find, often cost something like €2,50 untested for a DVD drive or even DVD burner. There's little reason why you should put up with messing with too little spare parts, it will suck your time and be more frustrating for little reason.

Outside the optical IDE drives, there are 'options' on using SATA drives with SATA2IDE adapters or using some PCI SATA controller, but I never messed with the latter and only have limited experience using an adapter for a harddrive (and none when it comes to optical drives).

It's possible the optical drives you gotten were defective when they ended up in your hands. I've had good experience in getting second hand stuff untested for cheap, but these were all gotten separately.

But my advice would be to simply get more IDE optical drives, these will not remain inexpensive and plentiful for long I think, so better stock up while you can and save yourself hours of frustration 😜

Here is something else to try :

Quoted from http://paulski.com/zpages.php?id=1812#Slow Spin-up

[6] Slow Spin-up

There will be times when there is both a good CD disk and drive and the BIOS Setup supports booting to a CDROM and has been correctly configured and yet that disk gets repeatedly by-passed as the set boot device. I believe that one reason for this can be that the CD drive just wont "spin-up" in either the correct or in a timely manner. If you cannot hear the drive spin-up to speed during the boot process then it cannot be read at this time (and even though it may be perfectly readable when accessed from an Operating System). You can try pressing the <Pause> key to halt the progress of the display and see if the drive starts to spin. If so all may be well and you would then press <ESC> to continue booting.

Disabling any quick boot options or specifying that only the CD and no other device is the boot device could be worth trying-out in the BIOS set-up.

I would also like to second Tetrium's suggestion as to acquiring/trying another drive . Weird incompatibilities do happen .

Somehow it fixed itself, now it boots from CDs without any problem