I am very beginner about DNN.  After DNN 4.0.3 Installation default.apsx (First time after installation) not loading properly, showing following error. Even, Administrator and Hosts login credentials not showing (which is displaying after first time installation).

First of all you should probably use the new DotNetNuke version 4.3.4. They say there are a lot of security bugs that have been fixed.

I have had similar problems but not sure how close the solutions might be. If you're able to log on with admin and host credentials and it's just a problem with some of the modules like links and announcements - check to see the version number. I was having problems with versions 3.03.xx which would throw the error "Currently not available." The reason was my webhost required I change my databaseowner ID from dbo to the one they gave me. They are supposedly coming up with a fix for this but meanwhile I was able to de-install those modules and install module versions 3.01 from an older dotnetnuke installation and all seems to be working well.

Your first post showed errors with the text/html files. Sometimes the home modules don't get set up properly and can be deleted and new text/html modules can be used in its place. Also without more information on your progress it's hard to tell.

Mike