Have you tryed to Test Configuration? What does it say? Meaby you have edited httpd.conf file or there has been some conflict. There's also a little possibility that your ISP has closed some of your ports. To check it, insert your IP and port here:
http://web.flavius.ro/
...or ask your ISP, as this tool cannot be always trusted.
I suggest you to install Apache again. If you're using some 2in1 package (for example: Appserv), forget it and install clean Apache from
apache.org. Do not assign any domains, leave all domains and hosts to localhost.
Im not sure if this will help you, but let's hope so.
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