On my 486 PCI mobo, the best LAN cards are either the Realtek 8139 or "Tulip" cards (like LNE100TX) believe it or not. Simpler is better cuz 486 PCI chipsets don't work very well.

Believe it or not, the noname card I tried has that same RTL chip on it and it didn't work. So it must be something to do with the clocking of the processor. I'll try another pb4 board with Am486DX4 100MHz (which is 25MHz x 4) plus regular ram and see what it is going to say about the PCI bus.

Btw, what is the model of the 486 mb you were referring to, is it PB4 also?

No I have a MSI 4144 that uses SiS 496/497.

Not sure what to suggest. It can be really tricky to get cards working in 486 PCI slots.... Just have to try a bunch of cards and see if any work. One thing that might be worth trying is forcing an IRQ to the PCI slot the card is in. NICs need an IRQ and sometimes these boards are too stupid to figure that out.

I never thought of fiddling with IRQ's but I'll do that this weekend along with cpu replacement. what would be the IRQ for vga cards? Is there a set from which vga chooses its IRQ on old systems or a predefined one I have to setup?

Also, I'll try to run cpu-z or something similar to it on this machine and see what info comes up.

Some vid cards don't need an IRQ. But you can assign one anyway. You just need to pick an IRQ that's free. IRQs 10, 11, 12 are likely available.

Hmm, seems like there is something wrong with the PCI bus on your board...

S3 Trio/Virge PCI cards are very tame and should work in any old PCI machine, no matter how buggy it is. 🙄
What happens if you set the CMOS back to default values and boot just with the video card installed? Did you try different PCI slots?

Network cards can be a bit quirky sometimes. For example, neither 3Com 905 nor Realtek 8139 can be persuaded to work in my SiS 496/497 board. I had to fall back to a Realtek 8029 instead.

I'm starting to think that those 3 pci slots are just 3 white pieces of plastic soldered to the motherboard. I get absolutely no response when I plug in the S3 cards along with the isa trident and the pc acts as if there is no pci card there. Although I do have pci bus reported inside win95 system devices and what is even more interesting, no resource conflicts which should come up if there is malfunctioning piece of equipment onboard.
It is most likely a physical hardware problem and not bios/sw related. If I plug only pci graphic in there is no-vga signaling from the beeper.