Hello there Thanks for helping me.
I installed Windows Server 2008 and .NET Framework 4.5. I didn't install an antivirus until the installation was completed. I turned off User Account Control.
In this case there was no need to create the user or give it permissions because the installer did it by itself.
It seems like the problem was the Remote Desktop Connection. A remote connection to windows may not set the permission correctly as local Admin.
Thanks & regards