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.

Use TreeSizeFree and run it as admin (this is very important to see hidden/system files and folders).

Now you see a nice overview of what is using the HDD space:

Check your system restore points. If they build up, you won't see them but they can eat a very large portion of the drive. You can configure your restore settings to control how much disk space they are allowed to use:

1. Click right on computer and select properties
2. Click System protection
3. Select configure
4. Choose max usage to limit how much drive space is allowed.