If you want to start Apache via XAMPP, but it won’t start, most likely another application listens to port 80. Very often this „problem-application“ is Skype. There are two possible approaches:

1. You start Apache before you start the Skype client.
2. You deactivate Skypes feature to listen to port 80 and 443. You can do this via the settings dialog. Just uncheck „Use port 80 and 443 as alternatives for incoming connections.

Now everything should be fine.