Use netstat -bano in an elevated command prompt to see what apps are listening on which ports.
But usually, the following applications use port 80 in Windows:
IIS
World Wide Web Publishing service
IIS Admin Service
SQL Server Reporting services
Web Deployment Agent Service
Stop any of the above applications that are running. You can do this on the Services tab in Task Manager.
As I am working in a corporate environment where developers faces firewall issues, none of the other answers resolved my issue.
As the port is not used by Skype, but by some other internal applications,
I followed the below steps to resolve the issue:
Step 1 - From the XAMPP Control Panel, under Apache, click the Config button, and select the Apache (httpd.conf).
Inside the httpd.conf file, somehow I found a line that says:
Listen 80
And change the 80 into any number / port you want. In my scenario I’m using port 8080.
Listen 8080
Still from the httpd.conf file, I found another line that says:
ServerName localhost:80
Change 80 to 8080.
ServerName localhost:8080
Step 2 - From the XAMPP Control Panel, under Apache, click the Config button again, but this time select the Apache (httpd-ssl.conf). Inside the httpd-ssl.conf file, find line that says
Listen 443
And change the 443 into any number / port you want. I’ll using 4433 as the new port number.
Listen 4433
Still from the httpd-ssl.conf file, find another line that says
<VirtualHost _default_:443>
ServerName localhost:443
And change 443 to 4433.
<VirtualHost _default_:4433>
ServerName localhost:4433
Remember to save the httpd.conf and httpd-ssl.conf files after performing some changes. Then restart the Apache service.
Best Answer
Things to be done to free port 80:
Once you start apache, you can sign into skype.