windows 7 - 750Gig Hard Drive shows full with only 315Gigs used

I have a Win7 laptop with a 750Gig C: drive. It came partitioned with 714Gig usable from manufacturer. I installed programs, music files, etc up to 285 gigs. As of a few weeks ago it showed 285 Gigs. Two weeks of house guests later and it shows HD is full. I deleted some files but it still shows 652 Gigs on this drive while there are only 285 Gigs on drive. Relevant details:

1. I am Administrator on laptop and have fair knowledge of what I am doing.


2. I did not restore from backup, restore from mirror, upgrade HD's or anything else that would have touched the partition structure. Just daily use as imaging machine and web.


3. I have checked partitions under disk administrator - no change, still partitioned with 714Gigs usable.


4. Have looked through computer C drive by hand showing Hidden files and folders - no change.


5. I have used JDisk Report to double check - it shows I have only 285 Gigs on C drive.


6. I triple checked with TreeSize run as Administrator and it also shows 285 Gigs on C drive - yet Windows 7 still shows almost full.


7. I used Windows 7 Utilities to Check for Disk Errors, and Defragged the drive. No errors shown and no change after Defrag.