Configured as per here?
http://th99.classic-computing.de/src/r/M-O/60151.htm

SRQ wrote:

BIOS gives an error and windows disk won't boot.

Some systems can't boot directly from CD-ROM, but need a boot floppy with the CD-ROM driver on it. Have you tried that?

yawetaG wrote:

Some systems can't boot directly from CD-ROM, but need a boot floppy with the CD-ROM driver on it. Have you tried that?

I think pretty much no 486 system can boot from CD-ROM. Perhaps some really REALLY late ones are the exception to that rule, but certainly not an ISA-only system, that would be a very early 486.
As far as I recall, booting from CD-ROM wasn't added to the BIOS until the late Pentium/Pentium II era.
My 'medium era' Pentium 133 (I think 1996) cannot boot from CD-ROM at least, and my 486 certainly can't.

Agreed. Software can help here. There is a version of Ontrack which lets you boot from Floppy but also optical drive. This works very well. I believe some boot managers offer similar functionality.

Scali wrote:

I think pretty much no 486 system can boot from CD-ROM. Perhaps some really REALLY late ones are the exception to that rule, but […]
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yawetaG wrote:

Some systems can't boot directly from CD-ROM, but need a boot floppy with the CD-ROM driver on it. Have you tried that?

I think pretty much no 486 system can boot from CD-ROM. Perhaps some really REALLY late ones are the exception to that rule, but certainly not an ISA-only system, that would be a very early 486.
As far as I recall, booting from CD-ROM wasn't added to the BIOS until the late Pentium/Pentium II era.
My 'medium era' Pentium 133 (I think 1996) cannot boot from CD-ROM at least, and my 486 certainly can't.

And there's that, too. I remember that our 486 (VLB board) could not boot from CD-ROM at all and also couldn't recognize any CD-ROM drives in the BIOS. My father had added a Mitsumi CD-ROM (supposedly ATAPI compatible, but it wouldn't work without its special controller card), and that also couldn't boot from CD-ROM. IIRC, the CD-ROM drive also lacked a Master/Slave jumper.

My best bet for the problem of the OP is that his CD-ROM drive is too new for any of the controller boards, so they simply won't recognise it. Furthermore, the Mitsumi board won't work without a suitable Mitsumi ATAPI CD-ROM drive, by which I mean a drive made for working with the card (later IDE Mitsumi drives won't work either).
To be able to boot from CD-ROM he'd need a controller card with its own BIOS chip with support for booting from any CD-ROM drive.

The BIOS doesn't have to detect the CD-ROM drive in order for it to work though (in DOS that is).
All you need is:
1) The CD-ROM drive connected to a compatible controller
2) The controller configured to a free IO port (interrupts aren't required, oldskool polling IO is good enough)
3) A compatible driver for the controller is loaded, configured for the correct IO port (if required, usually they just check the default ports for the first and second IDE controller, and find the CD-ROM automatically).
4) MSCDEX.EXE loaded, connecting to the driver

What might be a good idea is to download an image of a Windows 9x bootdisk. Because computers couldn't boot from CD-ROM back in those days, the floppy contains a basic installation of DOS and all the popular CD-ROM drivers. It will load them all with trial-and-error, and will usually get your CD-ROM drive working, if you don't have a super-exotic interface. Most IDE and SCSI drives should work at least.

I know a lot of people like to be period authentic, but I prefer to use a IDE dvd burner in my 486 and other retro pc's, also a 40gig hdd formatted via Ontrack software.
I can boot from floppy, cdrom, or from hdd into win95.
I copy what files I want onto a DVD-RW and copy onto the hdd from win95. Without USB and a network card it's the best way.

I think it was my Athlon system that was the 1st I could boot from cdrom, there really wasn't a need before that. You needed a boot floppy
to access the cdrom then could install windows or whatever.

Maybe the next step here is for the OP to post the autoexec and config files configuration.

Yea I use modern IDE DVD-RW drives in my 386 stuff without any issues 😀

yawetaG wrote:

SRQ wrote:

BIOS gives an error and windows disk won't boot.

Some systems can't boot directly from CD-ROM, but need a boot floppy with the CD-ROM driver on it. Have you tried that?

I mean the floppy won't boot :p

I'm confused on exactly where you're at.

1) The CD-R not being recognized by the BIOS is expected, as noted by Scali.
2) Have you tested it in another computer, either via an IDE cable or USB to IDE adapter?
3) Do that. If it fails, use another drive. If it works, you may be looking at driver issues, resource contention, chipset compatibility, etc.

SRQ wrote:

yawetaG wrote:

SRQ wrote:

BIOS gives an error and windows disk won't boot.

Some systems can't boot directly from CD-ROM, but need a boot floppy with the CD-ROM driver on it. Have you tried that?

I mean the floppy won't boot :p

Does it boot from floppy with the hard disk connected, or does it immediately try to boot off the hard disk? If the latter, check your BIOS boot order settings.

Have you tried replacing the IDE cable yet? If the system works with either the hard disk or the CD-ROM connected to the IDE interface on the motherboard, but not with both drives connected to it, then my first suspicion would be a faulty IDE cable. My second guess would be a faulty power connector or weak power supply causing the CD-ROM drive to not get any juice, but if the CD-ROM drive tray opens fine we can likely eliminate that possibility.

Do you have another IDE CD-ROM or DVD drive that is known to be good and that you could try? Frankly, being able to test all of the cards in another system to check whether they behave differently would be very helpful in eliminating possible causes...

Got it working, had to switch the IO board for another one so I could make the cable stretch.
As for the above: Yes I tried replacing it. The system simply would not boot /at all/ with CD connected to SB16 and no HDD connected.