Windows 7 No Disk Space after Disk Check Cancellation

Hey Guys,
I've been pulling my hair out trying to figure out what my problem is. Basically, we had an issue with the computer and so we force restarted it at one point about a month ago. After that, we started getting requests to run a check disk after every time the computer was rebooted. The check disks take 20+ hours for some reason on this computer, and we cannot afford to have it down that long since it is a work computer. We cancelled the disk check and afterwards we noticed that the hard drive was filling itself up. The computer has a 450gb hard drive and after a couple of hours it was telling us that there were only 2mb of space left (we have maybe 20gb of data on the computer total). This is the point in which I stepped in and ran a disk cleanup and deleted all of the old system restore points. It gave us about a gb of space so I left it alone (I didn't realize at this point what the problem was, just thought it was too much stuff on the comp). The next day the computer's user told me it was the same problem and I knew that she wasn't using all of the space that I had found so I checked it out again. Once again, it was giving me the low disk space error. I decided to download and install Windirstat to see what was taking up all the space. When I run Windirstat, it tells me that 430gb of the 450gb of space is "Unknown". After that, I shut it down and let it run the check disk completely over the course of a weekend. It ran for about a week after that, although still asking for a check disk every time it rebooted) and then I ran back into the same problem. I keep deleting things so that I can get a mb or two to try and run any programs. I'd really prefer not to reformat the system because we no longer have access to the key for the Windows 7 programming. Has anyone encountered this issue before?

Likely the file system was messed up by the forced restart, a rare but possible occurence.

So the unknown used space may be failed attempts to copy data over to repair the file system. This is why it's always advised to back up data before doing a Disk Check and of course data should always be backed up anyway against HD failure - which itself cannot be ruled out here.

I would test the HD with the maker's HD Diagnostic extended CD scan, followed by a Disk Check done from the Win7 disk or Repair CD's System Recovery Options Command Line which doesn't depend upon the OS on a potentially scrambled file system.