80 GB used disk space that actually shouldn't be being used

So, i have a hard disk (partition, actually) of 576 GB.
When i go to Explorer, i see 80 Gb of disk space that shouldn't be being used.
My disk contains only 23 Gb of data.

Does anyone know how to fix this?

Windows XP recognises SR so it shouldn't report the space occupied by the SVI folder as UNKNOWN. They are all accounted for in my system.

SR points are totally separate from hiberfils file.

It's easy to dip into the SVI folder without using extra tools.

With it unhidden and Simple File Sharing disabled, R click on System Volume Information folder > Sharing and Security > add your admin account to the list. Ensure there is at least Read permission.

Then you can read how much space is taken up in Explorer directly.

Hey!
The disk space that is used might be used by the windows system files like Page file, System Restore, hiberfil etc...! But that can't be upto 80GB... Might be you have some data that is hidden...! Try viewing hidden files and folders...! All the best...!

@killen: I have Windows Vista, and there's no SVI folder (maybe i already deleted it)

And it can't be hibernation files or that kind of things - i use Ccleaner