Windows 7: Unexplained low space on C: drive

Hi,
I've got a problem with my C: drive(which has Windows on it) slowly filling up. It started last night when all of sudden 3gb just disappeared from the HDD and by the end of the night I only had like 100kb left. I thought at first that there were some temp or junk files on there but after a few runs of disk cleanup and the app CleanUp! it was still going. That convinced me that there was some trojan or virus messing around with my drive information(system volume information) I did a scan with Malware, AVG, Kaspersky and Spybot and even though I found a few nasties getting rid of them didn't help. I'm at a loss of how to fix this, I didn't copy or install anything on C: and neither did I put a page file on it.And I know that having low space on your system drive can cause slowdowns and crashes. So can anyone help me out?

Please go through each option in this tut and use whicever is applicable, then let us know.

Hard Disk Space - Free Up and Recover

Do a disk cleanup....
Disk Cleanup - Open and Use

The tutorial actually has 2 parts :
From step #1 to #5, it does its nornmal cleanup. It will give you back some disk space.
From step #6 to the end, it will removed all your restore points except the most current one. That will give you back tons of disk space.
Warning : One problem. You won't have anymore " past " restore points to fall back to if you have any problem with the computer.
Therefore, you must make sure your computer is running fine before you do that step #6.

Hmm, tried all those steps including deleting the restore points and it did free up 200mb but that's still not enough.

Welocme
This article will probably help
Hard Disk Space - Free Up and Recover
In addition make a full scan with malwarebytes and your anti virus
Download and use windirstat, it will show HD usage.
http://windirstat.info/

I tried those steps already(some of them overlapped with that first link in the thread). And I did a full scan with AVG and Malware Bytes last night and it didn't help.

Try windirstat, it will show how all space is being used.

I've solved my problem, it seems I did have hibernation on by default and for some reason I couldn't find the file through the search but windir picked it up as taking 2.8GB space. So I turned off Hibernation mode and the file was gone.
Thanks for the help

Glad that the forum could help
Use that Windirstat to check for HD usage. I use it too.

If you had gone through Brink's excellent tut I linked in my first post, dealing with the hibernation file is included in it, but obviously you didnt. Its difficult for helpers here if OP's dont follow instructions. Anyway, glad it worked for you.