Open cmd and type the command below.
netstat -o -n -a | findstr 0.0:80
Last column of each row is the process identifier (PID)
You can find the application that reserves port 80, using taskmanager services tab or just type tasklist
in cmd.
Then follow this link: http://www.ttkalec.com/blog/resolving-yellow-wamp-server-status-freeing-up-port-80-for-apache/