That means what it says - port 8080 is in use - do you have Tomcat running on this server? That also uses port 8080. Either stop Tomcat, or change the port that Mendix is running on.
To do this in the Modeler, go to Project... Settings and go to the Server tab. Change the port in the HTTP Port section to something other than 8080, like 8085.
In a production environment, you can do the same thing through the Service Console.
Note that you will then need to access the application on the new port, like http://localhost:8085
That means jetty is running on the background. In order to fix this you've to reboot your computer or kill the java process in your task manager.
Thanks David ... working now.