May be default port used by some other internal applications, Follow 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.

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.