What version of MVC? What version of Visual Studio? Is this an old project or a fresh one.
If it's a relatively new project, it may be easier to create a new shell solution with the authentication you desire - then pull in your models, controllers and views from the old solution.
If it's a VS2013 MVC 5 project, you may be missing the
public partial class Startup
class in your root on the application.
If you create a new empty solution, you can compare what's there and what should be in yours.
HOWEVER.... you need to first read up on Simplemembership....