I have a Dell XPS 15 (2013 model L521X - Windows 7) with a capacity of 680.3 GB on the C drive.
But WinDirSat says that 217.4 GB of that space is <Unknown> and I can't access it! SpaceSniffer says that 215.8 GB is 'unaccessible space'!
The 'unknown' space is getting bigger by at least 1 GB a week – given the rate of increase, I think that this problem has existed since I got the laptop in 2013 or soon after. My laptop is now out of warranty and the explanation from Dell was laughable – they said that this amount of unusable space was normal!!
Has anyone experienced this – or know of any solution other than the ones I have already tried?
The 217 GB of Unknown space is definitely not system restore points. I have never set any restore points and have gone through the process to delete all restore points.
WinDirSat and SpaceSniffer don't list any files that are in this space – so there are no files I can delete. I have used CCleaner and the Windows Disk Cleanup to delete unnecessary system files.
I noticed that when clicking on the 'Cleanup System Files' button (in the Disk Cleanup), the progress dialog gets stuck on 'System error memory dump files' and then gives up. Perhaps there is some sort of logging or memory dump that is stored in an inaccessible directory
I don't have any other problems with the HD, RAM or Windows. Although I did have some problems when I first got the laptop with the Webcam not being correctly connected to the USB and got a couple of blue screens.