Please try to add following code in web.config and restart it:

 

 

or

 

When you launch the application, a little info mark appears at the right bottom of your screen telling you that the local web server was started and on wich port. You should compare that port to the one that appears in your browser. If they are different, an anti-virus could be responsible for that problem. Another place to look is your host file. Some software tweak this file and can make your localhost disbehave.