complete internet traffic halt/failure

Hi folks,
I have a really weird situation.

I have a server running Windows 2003 R2 standard server set up with the
following:


DHCP server
DNS server
NAT routing and remote access


Two network cards:
first card: attached to DSL modem/router, automatically assigned IP address
by DSL router; public interface of NAT

Second card: fixed IP address, 192.168.16.2; private interface of NAT


For several days everything worked great, server and everything attached to
it had Internet access. All of a sudden, last Friday, nothing works.

I can ping the public and private interfaces and the DSL modem from any
computer on the network. Using the DSL modem diagnostics, I can ping any
address (or URL) on the Internet.

When I attempt to load a web page, there is no connectivity. When I use the
command line and attempt to ping IP addresses on the Internet, there is a
failure. When I use the command line and attempt to ping the URL, DNS
resolves correct IP address but cannot successfully ping.

If I hook another computer directly to the DSL router, there is no problem
with Internet access.

LAN is completely functional

Any ideas what's going on with the Windows 2003 server?