I'm afraid I already have a thread running on this, but no replies since yesterday and working onsite and getting desperate.
SBS 2003 server, 2Wire ADSL router, 2 network printers and 8 PCs connect to two switches. The server sees four PCs and not the other four and cannot ping them. Nothing obvious in the server event log and all automatic services running.
I stopped and restarted the DNS server service and this brought one back, but two still can't ping the server, and the other reports the destination host unreachable.
I've rebooted the server and the PCs, ran Combofix, Malwarebytes Pro and SEP on two of the PCs, but no infections were found.