The AUI port on the ethernet card provides power out to run the transceiver, you could check there is DC present (can't remember if it's 5 or 12V) when the computer is running. Should be easy enough to find the connector pinout using Google.
The power will probably be via a fuse of some sort, so that could be a possible problem.
Last time I used an AUI transceiver on a Quicknet 2000 card, one of the ground pins on the D-range connector was not connected to ground, so I had to modify the card slightly in order to get the transceiver running. Might be worth checking that as well.
