Error: It appears you have another web server already running on port 80 on Windows

To troubleshoot this error you can try a freeware application that can reveal which programs are using port 80 and port 443 (also needed). You can download it from here:

Unzip package and run the cports.exe program as *administrator (right-click it and select ‘Run as administrator’). This little program will list all the ports that are open and by what processes with more details to investigate. You should be able to arrange items by port number by clicking the Local Port column. Scroll down to port 80 and port 443 and double click the entry. A detail page will show what is using the port.