Losing PCs from Network Neighbourhood

Hi, have a Windows 98 SE PC. Its set up to run a couple of batch jobs
periodically using the net use command, it also has a dial up connection
that periodically dials up to send/receive orders.

It appears that after either the batch job runs or the dial up connection
connects, it loses all the Windows PCs from Network Neighbourhood (except
for the Netware servers), but it is still possible to ping all machines on
the network.

A Master Browser is correctly configured on the network. TCP/IP, file and
print sharing and Client for Microsoft Networks and Netware client are
configured on the 98 PC. IP is the default protocol for the network.

Have also tried different network card, patch cables both PC and Switch
sides of network, and different port on switch.

Anyone have any ideas please??

Thanks, Steve.