repeating detection of nic

I have a win98 first edition and a dec nic card.
This problem is intermittent. It detects nic a number of times even you have already installed the rigth driver. And sometimes it found the network and sometimes does’t.
I have tested nic, cat 5 cable, removing driver and reinstalling but still won’t work.
Not sure whether it’s the mainboard or there is a patch for win98. or this is a know problem.

Thanks.