Pentium pro 200 mhz

This is a little bit hardware and networking, I stuck it here.
I have -zero- connectivity for my pentium pro witch used to work fine.
I have tried multiple NICs in each of the 3 pci slots. Nothing.
I cannot so much as ping the router or connect direct to modem.

Not even a packet. And when connected direct to the modem, the inet activity light flashes in sequence with the modem, even tried stuff like tcpdump to see if anything was coming across. Ifconfig shows zero traffic up or down.
I hooked someone elses computer up to my router and typed in the ip and the admin loggin window popped right up, the same with the modem, DHCP set the connection right up.
Also tried all the 'dsl' distros I have, boot up and fail to find a network. Finds the card just fine, local loopback is all that gets set up now.

Any ideas? I'm starting to think it's some component on the motherboard.

One more question... I have read quite abit about usb connections and STILL am not clear if any old (2.0 at least?) usb port will work for network connection or do you need a special usb nic port or card.

If you've tried several cards in all the different slots then it's my opinion that the mainboard is faulty, especially since another computer works perfectly when hooked to your modem.