I'm using XP. My hard drive is 40GB. I've always only used around 10 or 15GB at most. However, I've noticed that I have 31GB used, which is ridiculous - I don't have that much stuff! I've counted all the content manually and it reaches around 12GB, just as expected (and always has been). There's definately something wrong.
I think I read a virus description somewhere before; one which is related to false hard disk space estimate. I've searched long and hard without success for any information. Does anyone have any info on this? It's possible that a one-liner answer will solve my problem, but thanks for any help!

download spacemonger

http://www.werkema.com/software/spacemonger.html

what does it show?

Thanks for the fast reply! Yeah, space monger helped me see what space is being used. Well yes all the space is accounted for now; I am using all that 30GB. But I've lost track of the space I'm using because windows isn't showing me the correct amount of space taken up by specific folders.

Example; I have a folder called "Music" and a few subfolders.

When I click to view the properties, it shows "Music" as having only 488MB. Then when I select the subfolders and view the space they take up, it shows 5.27GB! I don't understand. I've never had this sort of problem before. Could there be some sort of compression issue or something? But then why don't the disk space properties in the music folder match the contents of that same one?