Newbie on W2k Server and zywall5 vpn appliance

I have a W2k Server SP4 that refuses to respond to any pings or attempts to
map its drives via a vpn tunnel using zyxel vpn client. While other
workstations (xp, w2k, win98 client) within the lan work flawlessly, all
ports on the server are just not responding even though that aren't any
firewall software installed. However, it is able work without problem within
the lan. The configurations are:

Server
Windows 2000 Server SP4 Ver 5.00.2195
Norton Antivirus corp ed ver 7.6

Client
Zyxel Remote Security Client Ver 10.7.1

Any recommendation?