Did you already try reconfiguring your card using 3c5x9cfg in MS-DOS mode? The string "3Com EtherLink III ISA (3C509/3C509b) in ISA mode" seems to be the name of the network driver, but I wonder what 0000 means. If that should read the I/O base address, something is bad, possibly the EEPROM on the card is corrupted. This is what 3c5x9cfg is supposed to initialize.

"No IRQ conflics" sounds fishy.

This card can be run in PnP or EEPROM mode. Given general state of PnP on 486 hardware and in Win95, I'd thoroughly recommend running it as non-PnP in EEPROM mode. Set it to IRQ 10 or 11 (usually free, but do check first) with DOS config, only then try getting it running in Windows.

dionb wrote on 2021-01-17, 12:54:

This card can be run in PnP or EEPROM mode. Given general state of PnP on 486 hardware and in Win95, I'd thoroughly recommend running it as non-PnP in EEPROM mode.

I am quite confident that "in ISA mode" means the card is already set to non-PnP in EEPROM mode. If the card were in PnP mode, it should read "in PnP mode" instead. If the OP is extremely unlucky, the card is "in EISA mode". In that case, it only properly works in an EISA mainboard, and the official tools are unable / unwilling to rewrite the EEPROM to ISA mode unless you plug the card into an EISA-based computer. 3c5x9cfg will tell you if that is the case.

Quick googling indicates that there are some test points on the card that can be used to force it into ISA mode even if the card is in EISA mode, which might enable reconfiguration without an EISA mainboard.

mkarcher wrote on 2021-01-17, 12:24:

Did you already try reconfiguring your card using 3c5x9cfg in MS-DOS mode?

mkarcher wrote on 2021-01-17, 13:09:

dionb wrote on 2021-01-17, 12:54:

This card can be run in PnP or EEPROM mode. Given general state of PnP on 486 hardware and in Win95, I'd thoroughly recommend running it as non-PnP in EEPROM mode.

3c5x9cfg will tell you if that is the case.

Unfortunately I can't even get the utility to start. It gives me the copyright string and hangs. Can't get it to work through the install program either.
Could this mean the card's EEPROM is corrupted?

Possibly, but could also be a major I/O range conflict. Do you have another system with ISA bus? See if you have same issue there too. If so, card may be at fault, if not, it's a conflict in that specific machine.

dionb wrote on 2021-01-18, 00:48:

Possibly, but could also be a major I/O range conflict. Do you have another system with ISA bus? See if you have same issue there too. If so, card may be at fault, if not, it's a conflict in that specific machine.

Unfortunately the only other thing I have is a Compaq Portable, which is so old I'm not even sure it's capable of using the card.
My BIOS also has no way to manually set interrupts and whatnot.

I might just look for a PCI ethernet card at this point, haha.

bevist wrote on 2021-01-18, 00:21:

Unfortunately I can't even get the utility to start. It gives me the copyright string and hangs. Can't get it to work through the install program either.
Could this mean the card's EEPROM is corrupted?

In case the 3c5x9cfg utility gets the I/O base address from the EEPROM, and tries to access the card at an invalid base address, like zero, it might disturb essential mainboard components and hang your system.

The procedure to recover from invalid EEPROM contents is described here. It seems the marking "E1" is not present on the 3c509TP(O) cards, but it is obviously the two big pads next to the ROM socket and the small 8-pin chip (the EEPROM). Shorting these pins during power-up should cause the card to ignore EEPROM contants and fall back to a default configuration which allows the card to be properly reconfigured to valid EEPROM contents. You can make sure that shorting these pins does not short your whole PC by testing that the left pad has continuity to the upper left pin of the boot rom socket (ground), bot the right pad does not have connectivity to the lower right pin of the boot rom socket (+5V), while the other end of R8 has connectivity to +5V (that lower right pin of the boot rom socket). The terms left/right/top/bottom in my previous sentence assume an orientation of the card with the ISA connector at bottom, the slot cover at the right, and the boot rom socket towards the top left corner of the PCB.