Win2k Server loses connection to public network

We have a problem with a web server, it will randomly lose its connection to
the outside public network.

Details:
1. Windows 2000 Server fully patched
2. 3 NIC cards:
a. Internal 10.0.0.0 network
b. internal 172.16.0.0 VPN via SonicWall
c. Direct to Cisco Router and our outside ISP service
3. relatively new Dell hardware

When this happens only the connection to the outside fails, the other two
NIC continue to function normally. Stopping and restarting that NIC will
correct the issue (temporary)

We have changed NICs and rotated the three networks around all of the NICs
with no effect.

We have also looked at the "Power" options and no hardware is set to "Sleep"
when inactive.

The problem seems to be more prevalent on weekends and nights, ie periods of
low web activity.

Does anyone have any ideas????

Thanks....RDK

Folks....A correction, the problem server is Windows 2003 Server Windows
2000 Server.

Thanks...RDK