Windows rejects admin password when i select 'run as...'


In Runtime
When logged in as power user and wanting to install/uninstall a program, Windows sometimes rejects my admin password and so i have to purposefully go into admin to perform a quick and simple operation.

Also, when i have tried to access the file in admin that i want to install under c:\documents and settings, Windows says that it is not accessible. For admin?!!!

Why is admin restricted? I also cannot even delete songs or videos in my power user account. What is going on?