I think I should be giving more details. I tried to view the disk in an other NT4 after this and the partion was not seen as NTFS but unknown. So I wanted to test if this problem was cronical and cloned an other NT4 disk and connected to a windows 2000 server, guess what ? after removing it from 2000, it was not booting as a NT4 anymore. I just learned that windows 2000 had NTFS 5.0 and NT4 had 1.1 and windows 2000 would, without any warning, change an old NTFS to new 5.0 version. This may be the problem in my case. Here comes a new question then, can I downgrade a partition from NTFS 5.0 to 1.1 or another solution may be changing the ntfs drivers of the NT4 to NTFS 5.0. I know that SP4 does this but how can I apply a service pack to a nonbooting system. May there be another way ?