This conflict has already been well documented but if you don’t know that Skype is the culprit, it’s pretty hard to find in a Google Search. I’ve decided to post here and include a few key words that might help some people trying to search out the answer.

The WAMP taskbar icon on my machine recently went half yellow and Apache didn’t appear to be working. When I visited localhost, all I got was “this page can not be displayed”. The culprit: Skype. Both applications use port 80 so Apache won’t run if you have Skype automatically loading on start-up.

To fix this problem, close Skype and restart your WAMP services. You can then re-open Skype.

Discussion on the WAMP forum