If you're having issues with your ASP.NET website startup, it could be due to a number of things. One way to debug this is to use the development server.
The development server is IIS Express, which comes with Visual Studio. When you start your website in Visual Studio, it runs IIS Express and your website on your local machine. This can be helpful for debugging startup issues, because you can see exactly what's going on.
To use the development server to debug startup issues, open your website in Visual Studio and select Debug > Start Debugging or press F5. This will start IIS Express and your website. You can then use the debugger to step through your code and see what's happening.
If you're still having issues, it could be due to a configuration issue. In that case, you can check the event log or the applicationHost.config file to see what's going on.