Administrator privilege with out the privilege!

I am useing Vista and it tells me I do not have administrator privilege when I try to set my default email program, delete only some folders(nothing important most empty), and some other random things I have tried to do. I only have one user set up on my computer and I am set as the administrator. My computer has never even had a password to protect it????
I dont know why I am having this problem it just started recently.