[Where did my free space go]

Yes, thank you.  After restart it reports 58.3 GB used and 39.7 GB free.  So at least 8-10 GB has gone missing.  I really have no idea what to look at next.

[Where did my free space go]

I was cleaning up my HDD that had 50 GB of free space and 50GB used.    A couple of the files were around 7 GB in size.  

  Defraggler ran for a few hours, and now reports that I am down to 25GB of free space.   What the heck happened?  How can I reclaim the free space that I had originally?

Thanks for any help!