One common reason the Apache configuration file (/etc/httpd/conf/httpd.conf) stops responding is that it has been edited with a DOS editor. DOS/Windows programs use a carriage return and a line feed to designate an end of line. Linux uses just the line feed character. When a carriage return character is located at the end of a line in a Linux configuration file it can cause the application that uses that configuration file to not work correctly, or even prevent that application from starting. These carriage returns will sometimes appear as ^M at the end of a line.

To avoid this problem, you should always edit the Apache configuration file with a Linux editor (such as vi or Emacs), or using the HSPC control panel with "Unix (LF)" line breaks selected.

See the article "Removing Carriage return characters from a Linux Configuration File" for instructions for more information.