If you tried to run the IIS or restart and you got an error exception occured, this means that another application is using port 80. To fix this, you have two choices, either to change the port for the IIS or check which application is using this port. If you gonna go with the second option, either there is another web server installed (i.e. apache or tomcat) or another program like Skype yes it use the port 80 if you choose on its connection option to choose the port 80 as alternative port. So check these software such as P2P because you may spend hours figuring what is this application and at the end you will discover it is just a chat software 🙂