Defrag & Space on Hard Drive

My 8300 has started to slow down.  I ran all of my spyware removals and did remove all that were found.  The computer is still sluggish.   Windows Explorer hangs and doesn't respond.  It takes several seconds to respond to commands.

My hard drive 'properies' says I have 9 GBs free.  I have moved many of my .jpg's and bmp pics to my external (backup) drive.

My question/problem is this.  After moving these files I did not gain any drive space.

Also, I did a defrag (several times) but after it 'defrags' and I click "analyze” , it tells me I should defrag again.

Can anyone help me?

Thanks

Stu