Windows not showing real free space amount on hard disk

I use Windows XP professional SP3 with a 500 GB Hard disk partitioned as
C (300 GB0 and D ((200 GB).

Yesterday I went to C properties to do a disk cleanup (after cleaning all temps, defragging etc...) and to my surprise disk C shows an incredible
80 GB used space when in fact it should be only 13 GB as I have always noticed. Disk D shows the correct amount of used space as 11 GB.

I recently deleted like 8 movie copies (each 4.7 GB) from my hard disk (they are too large to go to the Recycle bin so they are erased on the spot).

I have not installed any software in the past month (all softwares that I have installed are on partition D) so I only have the system files on C and 2 or 3 applications totalling about 13 GB.

I don't know why windows explorer shows 80 GB on C and I am looking for help to fix it. I googled the issue but only found related issues from years
2000 thru 2008 giving different solutions (but the issues weren't exactly like the one I am experiencing althought they were all related to windows not showing the correct amount of disk space.

I have searched for files larger than 1 GB with no results, none of my docs, pics, videos exceed a few MB. I need help to fix this.
Thanks

 

Have you emptied the recycle bin yet? 'Tree Size Free' is a good app to check what's using the space. There's also 'System Restore, which uses %15 HDD space of the total on XP IIRC. There's also the 'hibernate file' which uses the same amount of space as your RAM.

 

I have always set System restore to only 1% of space and when I clean I delete all but the most recent restore point BUT I don't use System Restore at all, I use Acronis True Image and I have backups of my entire system on an external HD that I create every week but I am trying to fix this without havin to go back 1 month to the last backup (I was lazy and did not backup for a month)

I also don't use Hybernate (disabled) and also just in case searched for the Hiberfile.sys and found nothing.

 

This tool can give you some more info on what is taking up your HDD space. You may have files in directories you weren't aware of.

http://windirstat.info/

 

Thanks to everybody their help was very appreciated, I installed the TreeSizeFree (audidoggie) and could not find anything strange (by the way this application is a little average does not go deep) appreciate it anyway.

Then I downloaded and installed the WinDirStat (thisisu) and this one was thorought and i could see instantly on the list that Drive "C" had 80 GB and when I opened C to see the files I saw a .dat file (64 GB) from Diskeeper (the automatic defragmenter that I have used for years and the best in the world at it).

I was very surprised as to the size of that .dat file , this is the first time I see a .dat file of more than some MB but this one was huge at 64GB and I don't know what data contained and how it was created (Diskeeper never created a .dat file of this size) but any way I deleted that file from the interface of WinDirStat and inmediately the C size came down to 16 GB
(the normal size I have had for long)

Problem solved !!! thanks to you both, you gave me the correct application to use but WinDirStat was more detailed althought a little complicated and a bit confusing at first but I did not have to go into details I just saw the Diskeeper .dat file of 64 GB and inmediately I thought "that's it, that's the culprit" and deleted it on the spot.

Now I am going to contact Diskeeper about this to see if they can provide explanation.

Thanks again !!!!