How Can I Solve a Privilieges Problem?

Hello everyone,
I´ve been dealing with a lot of struggles to install Itunes. When I execute the install setup i get this message "Service Apple Mobile Device Service failed to start. Verify that you have sufficient privilieges to start system services.".
I have tried every solution that I found on the Internet, like unistall and reinstall, extract with WinRar and then install the Apple Mobile Device Service, you name it. I even rebot my pc!
I really can´t comprehend what´s happening because I can install every other program, even Quicktime Player.
So PPPPLLLLLEEEEAAASSSSEEEEE can you help me!!!!!
Thank you!