To find out which process uses a certain TCP or UDP port you can use a tool called netstat. Netstat is a command-line tool that displays incoming and outgoing network connections, routing tables, and network statistics.
So to determine which process is listening on port 80, go to command prompt and type
netstat -aon | find ":80"
In the fifth column you get a process ID, from which you can then find a process in the Task Manager (that has to be configured to show PID column).
For more information about netstat see http://en.wikipedia.org/wiki/Netstat.