When I started Apache I saw these errors.

$ (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
Unable to open logs

This was puzzling to me since Apache was starting fine before. Fortunately on this forum thread, Failure Message starting Apache, one of the respondents had diagnosed the problem.

I’ve had the same problem. I noticed that when I reboot my computer (running XP pro), sometimes Apache worked. Then, I change the port to 3128 and it worked. But, then I was illuminated by God, and do a netstat -ao (-o displays the PID) and discover that Skype was listening in port 80 instead of apache -that is, I have both set up to run at startup, thus, if apache started first, it will have port 80 available, and Skype not, and vice-versa-. So my solution was to remove Skype from startup -I don’t use it too often- and make apache (and myself) happy by making port 80 available.

All I had to do was stop Skype and everything was fine. Too bad TcpView was not able to tell me that Skype was using port 80.