I have observed this problem with NTFS 3.1 quite a few times under Windows XP. But so far not in Windows 7. I guess MS should update this filesystem with something even better.
Is your HD a seagate drive? if so it might have been hit by the bug. Do a search for Seagate bug. Heh, i have been hit by this stupid bug and now i gotta do some trick and try and recover my 500Gb drive, that or send it in which is still under warranty, but then i'd lose all my data on it, so F that!
Well so far I know DFSR (Distributed File System Replication) is in the pipeline for Windows 8 and that's another story. NTFS 3.1 will stay intact :/ I wonder what happened to WinFS. MS can take the best of popular filesystems like EXT4, ZFS, QFS also including NTFS and give us a really really well working filesystem keeping backward compatibility. I am looking forward to Windows Next Next to bring this kinda change. Moreover I am in agreement with HelpMe for pointing out the Seagate HDDs. I have lost some large volume Seagate HDDs which were just 3 days outta warranty. :/