BleepingComputer.com: Hard Drive Space....Missing

Hello,
I have 160 gig on my 12 month old lap top. That is what is says on the packet but less with the bundled stuff.
After normal use and browsing and downloading pictures and music etc it stabilised at about 125 or more. But for some reason it seems to have "lost" about 20gig for no apparent reason. I think my last laptop did the same.
In both cases there was a reasonably high % of freee space but lost a chunk of free space almost overnight.
Any ideas please or suggestions.....not to concernig at this point but just can't figure it out.
Has the disc been partitioned or similar? How can I investigate?
Many thanks
John

Hi,

• Double-click on the "My Computer". This will open the "My Computer" window.
  
• Locate your hard drive. This will denoted as "Local Disk (C:)" on most computers.
  
• Right-click on your hard drive icon and select "Properties". This will open a window that displays all the information that you need about your Hard Disk.

What are the used/free space numbers showing as?

Download a program called Treesize, this indicates where you harddrive space is being used. Download Link