Just came across an issue where I started WAMP, but the icon went orange instead of green. Hovering over the WAMP icon in the System Tray, I saw a message like this:
local server – 1 of 2 services running
Turns out that I had Skype running and it looks like the port that Skype uses (80) collides WAMP. Closing down Skype and restarting WAMP did the trick.
Also found a reference on the subject.