Use something like this : http://www.01net.com/telecharger/windows/Utilitaire/systeme/fiches/104443.html

or win dir tree, or space sniffer

maybe it's in your system files ( windows cache, system volume info… ). You may try CCleaner also.

As weird as it might sound. Erase all your temp files using CCleaner and then defrag your HDD using Defraggler or some sort of defrag tool. I had this bug on my previous windows installation and the defrag gave me the reserved space back.

Corrupted NTFS entry is the most likely culprit. From the start menu hit run and type cmd. That will get you a command prompt. The type chkdsk c: /B and hit enter. It should tell you it will need to reboot and then it will run a full scan and repair of EVERYTHING on the drive. Do note that it can take several hours but it should fix the problem assuming you don't have a drive that is physically damaged.

Have u tried removing shadow copies? U right click on the disk in explorer and choose properties and its somewhere there.

run cmd.exe as admin, type sfc /scannow, hit enter, if that doesn't work then you need to format/get a new hard drive

If nothing is resolved by tomorrow when I get home from work. I will ask one of the techs where I work to see what he would recommend doing. If the data is important enough, I would pay for the shipping both ways and have a tech at my work get all the data off for you.

Maybe some hidden C:\found.000 kind of folder due to chkdsk. I'm not sure but I saw them mentioned in chkdsk result sometime and see it when I boot in Linux.

S.M.A.R.T. is all OK of course ?

CrystalDiskInfo

Try going to the recovery console and typing FixMBR

Go to disk management.

Right click w/e partition is your OS partition.

Extend volume.

kdone.

try using http://joshcellsoftwares.com/products/uncleaner

have you scanned your disk? few years ago i was having virus which was making my disk space a lot smaller than in reality,
u can use free software like avast, malwarebytes anti-malware and spybot search and destroy

clickable link

Did you have an AV before this happened?

WinDirStat is a fantastic little program that lets you visualize your HDD space :) I use it all the time.

What about the "C:/Users/username/AppData/Local/Temp" folder? Maybe disk cleanup left some stuff there...like everything

Did you try a HDD management software like HD Sentinel?

So,you only had 1 partition with 1TB on it?

Hit the start button and type Windows Disk Management. You may be able to enlarge the partition to use the full disk space, or repair the likely damaged partition.

You should have reinstalled as soon as you lost power during partition creation. I suggest backing everything up right now and reinstalling. Currently, you risk losing data that is written to the drive.

Funny thing i had a similiar issue like this last week, i installed quite alot of games on steam, i had 100GB left out of 1 TB, when in reality i should have more. The size kept dropping, by the time i got 60GB i thought "Maybe i should delete a random game on my library after giving it a shot." So i did that with red orchestra 2 multiplayer edition, i was lagging extremelly bad on my first match with 32 players and was being spawn kill non stop in a king of the hill match or w/e (more of a reason to remove the game tbh).

So i removed it and checked my HDD and it went up by 200GB, it's now sitting at 260GB free space.

I tried software to defrag, clearing cache files and temp files, tried some other stuff, it doesn't seem to work. My guess is that you should make a backup of the software you have and wipe it clean then copy paste back. Or try copying the heavy software one by one untill you catch the troublemaker.

I had a similiar issue with FEAR 2 3 years ago, the game was occupying 6 times more room than it should on my old laptop, when i removed it, the space was randomly increased by alot.

It told you that you need to initiate a disk? Sounds like the partition is damaged beyond Disk Management's ability to recognize a valid partition. Make a backup of your important data, and repartition your HDD. Then reinstall Windows 7.

At this point, saying that you want to fix the problem but you don't want to repartition/reformat/reinstall is like saying that you want your appendix removed but don't want any surgery, or that you want to drive across the country but want to do it on foot.

Consider making a backup image of the drive once you finish your OS reinstall and installation of all desired programs. It is best to do this from a desktop pc with the backup being saved to a large external drive. For the actual imaging program, I like DriveImage XML. I make a weekly backup of my desktop hard drive to a 1 terabyte usb drive. It's a fast 250GB drive, while I have an internal 1TB drive for data. The backup drive is large enough to hold two rotating backups, so if I lose power during a backup and ruin both the new backup and the current OS installation, I still have my backup from the previous week to restore. If I were only working with a single backup, I would be without a usable backup until each new backup completed.

Use GParted. Start from the bootable disk and confirm what the available disks say there. You might be able to repair your partition. Of course, always best to backup important data before trying repairs etc.

Sounds like a faulty Windows or maybe some kind of virus. You need to format your HDD and install Windows again. And I suggest making 2 partitions for your hard drive - one just for windows and other one for everything else. If your Windows will break atleast you won't lose other data!

I would rescan your system for viruses... Use multiple scan tools not just Avast (try Malwarebytes, spybot search and destroy, and even Microsoft security essentials. Also use R-Kill before scanning (can be found on bleepingcomputer.com) You can also get boot disks from AVG, Kaspersky, Avira, Panda and others that will scan your drive without loading Windows (viruses can't protect themselves if they are not loaded). It seams that every virus scan picks up something different so relying on a single scan is not always the best idea. If you know what make your hard drive is, the manufacturer will normally have testing software available in many cases the programs provided by the HDD manufacturer are better than a simple chkdsk /r or /f (seagate and western digital also provide disk cloning and backup tools).