Cannot access http://localhost:12345

I'm developing a WebAPI project on Win8 using VS2012. It uses IIS Express 8, which is pre-installed. When my project is open in VS2012, I can access my app from IE, like so: http:localhost:12345/api/products. However, when I close VS2012 and then try to access the same URL in IE, I get the following error message:
"No connection could be made because the target machine actively refused it 127.0.0.1:12345"

I have opened port 12345 using Windows Firewall, but no success. In fact, when I go tohttp://localhost:8080, I get the same error.