Lost Disk Space on Windows XP

I'm not sure what's the problem with Windows XP but once in  a while, it doesn't seems to be able to reclaim disk spaces. I have tried everything and nothing works except for chkdsk. I have just ran it and I have 90GB more free of disk space. The process does take a while so do plan to leave your computer running chkdsk for an hour or 2. If you're not familiar with it. All you need to do is open a command prompt (Click on Start then Run and enter cmd then press ENTER) and run chkdsk.