I'm trying to make an application that replaces explorer.exe (by replacing the registry key Windows NT\CurrentVersion\WinLogon\Shell) and it asks for a password, if the passowrd is correct it continue by starting explorer.exe.
All is finished, the only problem is that even after starting explorer.exe by the application it only runs the explorer window (in this case My Documents) without any desktop stuff (desktop, taskbar).
I want the desktop to show, is there any arguments I should pass to explorer.exe?

Not going to happen with .NET. A .NET application required the .NET Framework in order to run, and the framework isn't loaded until Windows boots, so there's no way in C# to accomplish this. Also, this really sounds like a malicious action (in my opinion)