The apache error log said the port was in use. The probably occurred because Skype and Hamachi were both open and listening on the same port. I simply closed them, launched Apache, and reopened them to resolve the problem.
(OS 10048)Only one usage of each socket address (protocol/network address/port) is normally permitted. : make_sock: could not bind to address 0.0.0.0:80
no listening sockets available, shutting down