Restrict unathenticated users to access specific page without using ASP.Net Membership Provider

I'm working on an asp.net application, and I developed a custom user system (I didn't use the asp.net membership system).

Now, i want to deny guest users access to the whole application except from Login and  Registration page. All other files include the Login/Registration reside in the root directory!

How can I achieve it? I'm thinking if there could be a way of doing that in the Web.config or global.asax file, or otherwise

I'll appreciate your answers.