I second what rkauer says, i have seen a 4000 crash at 4.87v when i was using a old amiganet card, it was fine until i added the load with the transciever on the aui port, and that was just enough to drop it and lock up.
personally i like to see at least 4.9 on a expanded one.Also check the power supply to motherboard connector,its not unusual to find a pin or 2 expanded and not making good contact,and in bad cases the 5v pin has been hot and discolored.
good luck!
Mike
