Lost disk space!!

I have already read the previous thread about the Windows folder and its massive size. My windows folder seems to be taking up allot of room, 19gb actually. However, when i search the files, hidden files and all, I find that there is no one file larger than 3gb. In fact all the files total to be about 6gb including the hidden ones. Where is the extra 12gb? Could it be that the pie chart telling me about hard drive space is wrong? Btw I have only one partition on my hard drive.