If you make a request to your application, then "Application_Start" is launched? I do not think it will be launched before the first request.
Application level events only require the correct naming convention to work. Is your codebehind class specified in your Global.asax file?
<%@ Application Inherits="YourNamespace.YourApplicationClass" Language="C#" %>
(or)
Projectbecuase , global.asax.cs.
: - . , .
Edit
aspx codebehind
, ,
.
, :
HttpContext.Current.Response. → -
ASAX -