Open the network settings from the Apple menu. Under the Services tab, make sure that the server has a name. Make sure the setting to be a web server is checked. If this is the case, the /etc/hostconfig file should include the following line:
WEBSERVER=-YES-
Check the console for any relevant errors by choosing the Console command from the Tools menu in the Workspace Manager.
Attempt to start the server from the command line by typing the following command at the prompt (open the Terminal application first):
apachectl start
If there is an error about the server's name, set the server name manually by editing the apache.conf file (/Local/Library/WebServer/Configurations/apache.conf). The setting you will edit is "ServerName". You must replace "localhost" with an explicit hostname (for example, "joesbox.apple.com") Be sure to use the hostname provided by your network administrator or ISP. Also, uncomment the line by removing the pound sign (#) before the "ServerName" on that line.
Please back up the config file before making any change by typing the following command at the prompt:
cp apache.conf apache.conf.old
After saving the changes to the config file, try restarting the server manually again from the command line.