I have a similar problem, I'm running an 80GB NTFS Hard drive with a 70GB partition and a 4.6GB backuppartition. When i check free space on the 70GB partition, its only 3GB. But in explorer when I check the size of every folder in C, they add up to only about 26GB. So some 30GB are missing. I checked disk management and there are no extra paritions, and I havent reformatted the disk ever, and have included all hidden files. I'm using windows xp, Any ideas?