It probably doesn't matter, but what's the CDROM model?

Tried several brands and models, some old ones with 8x / 10x speed and some newer.

Try a different CD-ROM driver. Older CD-ROM drives don't work very well with a generic driver like videcdd.sys.

Try oak.sys or other manufacturer specific.

Still nothing. I think it's something to do with the Promise card.

Could be worth checking a different BIOS version maybe?

Have you tried hook up the cd-rom to an sound card ?

I had already thought of that because I have a SB32 with the port in the back but haven't got around to it yet.
I really would love to take advantage of the Promise card.

So firstly, old BIOSes don't "see" the CD and list it as a device, so that's not important and it can't boot from it. Some slightly later ones might just say "atapi device" in primary slave or secondary master slot. So even if your motherboard doesn't see it, the CD driver may see it.
Edit: derp, ignore above board taking a P166 should be recognising ATAPI devices. Early socket 5 mightn't though.

However, some HDDs especially any older/smaller than 1GB are a bit funny, and especially when you're using mixed manufacturers you may need to set slave present jumper as well as the master jumper on the primary master, and have CD set to slave as well.

Promise controllers are a PITA if they haven't got a HDD on they might not load their BIOS, and if anything is on the primary controller, put themselves in as tertiary, which DOS does not see by default, only NT flavors of windows will pick it up, or Linux as far as I'm aware. Not sure if there's a driver for those to bring them up in DOS. What is needed to get the promise card available in DOS is to leave motherboard, or other I/O car channels empty, put the primary HDD on the promise controller, then it will load it's BIOS over the systems HDD bios and appear as primary and secondary in DOS.

After some months I'm back on this again.

So now I have both the hdd and the cdrom drive connected to the Promise TX2 card (both identified on the card's bios), Dos is loading fine but i still can't get the cdrom driver to load. Tried two different drivers with no luck, autoexec just
says it can't find the drive (probably because it's connected to the Promise card and not the ide port on the board.

Any help folks?

See the sticky for other drivers to try, sbide.sys is normally pretty reliable.

I finally managed to have everything working and what happened is something I just can´t explain.

So after trying all possible combinations of ide ports/jumpers/ide cables I couldn't for the life of me get the cd-rom drive to get recognized.
I assumed there was a problem with the board and moved on to try and use a pci ide controller, the Promise TX2 card. Both the hdd and the cdrom where recognized by the card but i couldn't get a cdrom driver to work.

I tried to have the hdd connected to the ide port on the board and the cdrom on the controller but that didn't help either. After having tried a couple of different cdrom drivers with no sucess I was ready to give up on this but
before I tried one last time to use primary ide for the hdd (master) and secondary ide for the cdrom (master) and guess what, the board detected the cdrom and dos loaded the driver.

I'm absolutely sure I tried this before and the cdrom just wasn't detected at all.

But the journey wasn't over yet.

There were a couple of autoexec files on the hdd (from trying all the drivers) so I wanted to do it all from scratch with a clean installation of software.
I fdisked the hdd, created the primary partition and set it to active. Booted the system with a win98se floppy install disk which loaded the cdrom driver with no trouble but then when I tried to format the hdd, the format executable wasn't there.
In a glimpse I was taken too the late 90's and remembered I used to copy the format.exe from another source to that boot floppy. So I browsed the Win95 cdrom and found a format.com which I copied to the floppy.
Unfortunately that format command just didn't worked (/q /s with no arguments, nothing worked), it asked me if I wanted to proceed I would say yes but when trying to c:\dir the system would just give me the abort, retry, fail error.

So next I thought, well let's just start Win95 config and the drive will be formatted, boy was I wrong, as soon as I hit config.exe the system would say there wasn't enough space for the installation.
In despair I browsed the win95 once more and inside a folder found a oemsetup.exe file which finally started the installation, formatted and disk and now the system is finally up and running.

I know I could have installed dos first instead which would probably format the hdd with no problem but I don't have the floppies with me right now, which leads me to another question, is there a good reason to have a real dos installation
instead of the win95 Dos mode?

So far all the Dos games I tried worked flawlessly after rebooting in ms-dos mode but it's something I would like to take out of the way.

Sorry for the testament and thanks once again.

Probably most 1993 and later games won't have a problem. ... and there's lots of games prior to that which will work. ... games that are super picky are maybe going to have speed problems also on a P166MMX