Explorer can't see most of my C drive

[albatross32]

I have Vista and recently my system lost all settings and reverted to first install settings. I was then alerted to the fact that iTunes and all other music files have been deleted from my C drive. When I look in Explorer it says my C drive is 69.7 GB whereas it is a 1TB drive! 'Show Hidden files' has the same result. Why can't it see most of my hard drive? How can I restore it?

 

[albatross32]

Come on people there must be someone with an idea of what I going here!!