Why did my hard drive suddenly fill up? (Windows Vista)?

Three days ago, my 320GB drive had 140GB free, then yesterday, it unexpectedly dropped to 30GB. I downloaded a freeware program (Directory Size) that scans your drive and lists folders by how much information is stored in each, but it only found 160GB of data on my entire drive (which would have been about right up until three days ago). I then defragged the drive last night, only to wake up with 2GB free!! Obviously Windows is not reading the drive correctly....I scanned for Viruses and Spyware, but my system is clean....

I haven't even been using the computer much lately.... I've only done two minor things with it in the past month - About 20 days ago I installed Carbonite (which seemingly works fine) and last week I added an iMac to my home network (no additional software was installed on my Vista machine to the best of my knowledge...the only thing that has been shared between the computers was my iTunes library).

Any ideas? Thanks!

Why did my hard drive suddenly fill up? (Windows Vista)?computer repair

I suggest you use NTFS Active@ Boot Disk. This is an unbelievable resource for almost any Windows problem. I have had all kinds of PC problems, and it has been the most valuable. It will let you explore your drive with absolutely no restrictions. It has found things on my drive that I couldn't view with about 10 other commercial applications that I tried. It will give you the true story of how much space you're using and what is using it.