Defender install crashes windows server 2003 network

[Guest]

When I installed Windows Defender on a Windows Server 2003 SP1 server,
network PCs lost their network connections. The server can access the
internet, but client PCs can't. I cancelled Defender while it was doing its
check, uninstalled Defender and rebooted the server. But client PCs still
don't have access to the shared network drives, and they still have no
internet access. Client PCs can ping to the internet. Has Defender crashed
the DNS service? How do I restart it?

 

[Guest]

I gave up trying to resolve this, and rebuilt the server.