NETWORK NEIGHBORHOOD DOESN’T WORK

I have a 5 computer peer to peer network with an ISDN line running Win98. All computers work fine with seeing each other except for one. It will work fine for a week or so then all of a sudden it will not find anything in network neighborhood or any network shortcuts. My explorer will crash when I try to use Network Neighborhood and the network shortcuts. The ISDN line works fine everytime though and uses the network also. I use tcp/ip and netbeui. When I format and reinstall it will workgreat for another week. No viruses found ever either.