I can now confirm that the problem of the TV hanging when it scans the hard disc was due to the block size of the NTFS file system ! (I've used 8KB instead of the standard 4KB when I've formatted the disc for the first time.) I have reformatted the disc, this time with the default block size, and copied all original movie files back on the disc, and now the whole scan takes approximately 5 seconds, as it should.
I've wasted a lot of time trying to figure out the problem, because the symptoms are very strange. It seems that the TV supports perfectly a certain number of files, but not more files, or not certain files. So, after having used my disc without problem during months, suddenly, it has stopped working fine and became ill because I've added a file or two! So, the lesson is that you should never change the "allocation unit size" when you format a disc for a Samsung TV! Keep the default settings proposed by Windows. I hope my bad experience will be useful to others.
Note that after having reformatted the disc, I have used the Paragon Alignment Tool (
http://www.paragon-software.com/home/pa ... alignment/) to align the blocks of the filesystem with the physical clusters. Theoretically, that can somewhat speed up your disc. I don't think it's necessary for the TV, because by default Windows does not align the blocks. But that doesn't hurt.
Anyway, I've been lucky, because you've helped me much, zoelechat, and because I have received an empty disc for a couple of days from a friend, and I've been able to back my files up. Without that, I suppose I would have jumped on my TV! So, thanks again!
In the other hand, the R/W NTSF app doesn't work. It does something, and I see a flash when I launch it, but even after having waited several minutes, when I try to write on the NTFS partition, I see the "read-only filesystem" error. It's not a big problem. I don't need to access my discs with FTP, and I prefer the security of read-only NTFS partition, especially now that I know that NTFS is badly implemented in the OS of the TV. However, if a better solution to mount the NTFS partition in wr mode exists, I would like to try it. That may be useful sometimes.
Anyway, thanks again to SamyGO and this forum. Without you, the Samsung TVs are crap!