Skype interferes with xampp and wamp on port 80

When Installing XAMPP and xampplite it could not start. The Apache server it appeared to be a problem with using port 80.

When installing wampserver the port 80 test determined that Skype may be using it.

After closing Skype and the server was able to run and wamp came online displaying the test pages - working fine.

In Skype options: [connections] , there is a checkbox labelled "Use port 80 and 443 as alternatives for incoming connections".
This is our problem, so simply uncheck it and save. It may require a Skype restart.

You should now be able to start the WAMP, XAMPP or xampplite server again. If you still have trouble, try closing Skype.
It's also possible to configure Apache to use other ports if neccessary. See Apache docs.

There are some other net applications (like P2P apps, chat applications, Media Centres or, of course other webservers like IIS) that also sometimes grab port 80. It's a common method to get through firewalls when the normal protocol is blocked.

One way to test if 80 is in use
Ensure the expected webserver is not running.

At a command shell:
telnet localhost 80

What we want to see immediately is "Could not open connection to the host, on port 80" and a return to the commandline. This means that port 80 is not in use already, which means the webserver can now be started.

If you see anything else - especially a PURE BLANK SCREEN for more than a few seconds, it means that something is listening ... and occupying that port. Depending on the application it may be hard to quit, so press enter a few times, or just close the DOS box.
Now go and start shutting down net-type applications and services you may be running.