low hard drive memory

Hey, this is my first post so please bear with me.......
My hard drive memory is really low. I regularly clear my temp files which improves matters a little but not conclusively. I really cant understand why it is so low as i use an alternative drive for storing all large files such as music and photos, and do not play games so have no large programs installed. its showing 9% free but it should be over 50% i think.
I would be very grateful for some help here. Many thanks

Welcome
Three things to do to find the cause
Update your anti virus, then run a full scan
Download, update and make a full scan with malwarebytes

If Negative

Take memtest
Guide to using Memtest86+ - Geeks to Go Forums

If memory is ok test with clean boot
http://www.sevenforums.com/tutorial...ation-conflicts-performing-clean-startup.html
same for Vista