XAMPP PORT 80 is Busy / EasyPHP error in Apache configuration file:

Things to be done to free port 80:

1. check if skype is running, exit from skype
2. check services.msc if web deployment agent service is running
3. check if IIS is running, stop it.

Once you start apache, you can sign into skype.

Only one process can use port 80 at a time. Port 80 is the default port for web servers, so when you navigate to websites over HTTP, you are actually navigating to that server's port 80 by default (when you use HTTPS, the port is 443).

You can try to hunt down all the programs that are running on port 80, but there's an easier way that will work for development. When running XAMPP, click "Config" under "Apache". Replace Listen 80 with Listen 8080 and ServerName localhost:80 to ServerName localhost:8080.

Then, when you want to look at your masterpiece, navigate to http://localhost:8080 in your browser.

SQL Server Reporting Services (SSRS)
SSRS can remain active even if you uninstall SQL Server.
To stop the service:

Open SQL Server Configuration Manager.Select “SQL Server Services” in the left-hand pane.Double-click “SQL Server Reporting Services”.Hit Stop.Switch to the Service tab and set the Start Mode to “Manual”.

Skype
Irritatingly, Skype can switch to port 80. To disable it, select
Tools > Options > Advanced > Connection then uncheck
“Use port 80 and 443 as alternatives for incoming connections”.

IIS (Microsoft Internet Information Server)

For Windows 7 (or vista) its the most likely culprit. You can stop the service from the command line.

Open command line cmd.exe and type:

net stop was /y

For older versions of Windows type:

net stop iisadmin /y

Other

If this does not solve the problem further detective work is necessary if IIS, SSRS and Skype are not to blame. Enter the following on the command line:

netstat -ao

The active TCP addresses and ports will be listed. Locate the line with local address “0.0.0.0:80″ and note the PID value. Start Task Manager. Navigate to the Processes tab and, if necessary, click View > Select Columns to ensure “PID (Process Identifier)” is checked. You can now locate the PID you noted above. The description and properties should help you determine which application is using the port.