Windows 7 - Missing space on C drive

Hi
I have been trying to find a solution for hours.
I have 3 drives on my computer:
C: 298GB for operating system/program files (no pictures/files/music/videos)
E: 1TB for my files
F: 500GB for video

I can't account for 176GB on my C:drive. Right-clicking>Properties shows there is only 35.7GB of free space.
When I used TreeSize and Windirstat to analyse C Drive, both come up with 86.1GB of files but both can't find where the other 179GB is. (Windirstat identifies an Unknown folder of that size but can't tell me any more)
I have emptied the Recycle Bin; done three or four disk cleanups; deleted all restore points with no effect. I am still unable to locate or get back this missing 179GB of space.
Running Windows 7 Home Premium with SP1 / 8GB RAM / i7 860 processor
Have Norton 360 and used that numerous times to clean disks
Have "Rollback Rx" and have deleted all of my snapshots except 3

Can't do defrag on C because there isn't 15% free space. I forced a defrag (was 34% fragmented and at the end it reported 33% fragmented)

Can someone please help me get back my disk space on C drive
Thank you for any advice

Sorry - addition. This is screen shot of Disk Management

This will show you how to upload a screen shot - Screenshots and Files - Upload and Post in Seven Forums

Screenshot of Disk management


Have also noticed when I try to do a disk clean up it doesn't appear to actually remove the files?
As it scans C drive there is a "System Error Memory Dump Files" message in the window. It then goes away and is replaced with a list of files it can delete. I click OK/delete but when I come back and repeat the process the same files are there (but their total size is less than 1GB)

Here are the screenshots of TreeSizeFree and WinDirStat

Most likely 3 things:

1. The pagefile - C:\pagefile.sys (usually a hidden file). Windows will by default set this to something like 1.5x the size of your RAM, but you can set this to a fixed size. Definitely recommended if you have much more than 3 or 4 GB.

2. The hibernation file - C:\hiberfil.sys (also hidden). If you never use hibernation, disable and delete this file by opening a command prompt with admin privileges and typing powercfg -h off which should take effect immediately.

3. System restore points. Try deleting all but the most recent restore point (only if you're sure you won't need to roll the system back anytime soon of course). You can also limit the disk space available to System Restore through the Control Panel.

Thank you for the suggestions
1. found this file and it says it is 8GB (which is the same as my RAM). Don't know how to set it to a specific size.
2. Tried this but got an error message (tried with and without space)
3. Did this again (have done this 3 times now)
FORGET EVERYTHING!!!!!
I now have 196GB free space!!!!!!!!!
Just wondering if I had to restart computer to make changes take effect!!!
Whoohoo!!! EVERYTHING IS ALL GOOD.
Thankyou so much for all your help. I really appreciate the time and effort people here take to help others. Awesome!!

Great, glad it worked. The correct powercfg command btw is "powercfg (space) -h (space) off" but it's up to you to use it or not.
As for the pagefile, rightclick My Computer on your desktop or in your Start menu and select Properties from the context menu. In the window that opens, click on Advanced System Settings (on the left). Another window opens; click the first Settings button near the top and then (yet another window) go to the Advanced tab. Finally, click the Change button.
You guessed it: another window.
Now you can uncheck "Automatically manage paging file size for all drives" (if checked) and set custom sizes for the pagefile per drive (just leave it on your C: drive). Since you have a lot of RAM, a 1GB pagefile should be sufficient, so click "Custom size", enter 1024 and 1024 and then click the "Set" button at the bottom. This will prompt you to restart, but you can do that whenever you're ready, it doesn't have to be right away.

Anyway, glad the system protection settings did it for you