I have XAMPP installed on my PC Laptop for the occasional development I do when on the road. A while back I was trying to startup Apache through the XAMPP Control Panel, and Apache would attempt to start, but would always fail.

I finally realized that the culprit was Skype (must be a port collision). I just closed Skype and Apache started right up. As soon as Apache is running, I can open Skype back.

Hope this helps for any of you googling this issue online.