Internal Hard Drive almost full but I cant find half my files!?

Really need some help here, not much of a computer techy havent been able to find a solution for this yet as most people experience this with an external hard drive. My hardrive is almost full but half the files occupying that space are literally nowhere to be seen? Now surely if they were all deleted they would be in my trash or if that is emptied, the hard drive space would of been freed? I'm on windows seven, I have done all the show hidden files etc but still cant find! All my pro tools files VST's along with alot of hard work have just somehow played Houdini :(.. Any help would be greatly appreciated :)!

Snootchie bootchie!