A few weeks ago, My server had a strange problem: Sometimes all the PCs lost connection with the server, but meantime the server can access internet. That means physical network connection is good. After changing server's name. The problem disappears. But a few days after. the same problem comes back. I used NOD32 to scan the server, but nothing found. The server's OS is Windows 2003 small business edition. Does anyone has any idea? Thank you.

I am using windows server 2003 also, no problem for me. Try making continuous ping and observe. Event logs will also help you tracing what is happening to your network.