I'm having the same problem except I have 267 of 300 gigs used. I'm running windows Vista. If I open file explorer I can see the drive. When I click on it says there are no files yet when I right click on it and look at properties it shows 267 gigs being used. I saw that you mentioned something about raw but I'm not sure what you mean by that. I do have RAW photo files if that what you mean but I don't know why that would affect anything.
I recently had my internal drive formated and brought back to the factroy specs and after that I cannot access the external drive. My internal drive's format is NTFS while the external drive is FAT32. I'm not sure if it matters but I thought I'd mention it.
Any help would be greatly appreciated.