ad0 vanishes just before mount

Hello all,

At work, ad0 is not detected, neither on 5.4, nor on current
from 01/05/2005, or from 16/05/2005.
(erased bin etc sbin usr/bin usr/sbin and lib and libexec and rebuilt all
on another machine; mounted the drive externally and reinstalled all).

The kernel is properly loaded, but after that, the drive
vanishes: no detection. We fall in the manual mount.
of course no mount is possible on that drive.

N.B. acd0 and acd1 are properly detected and working
on the secondary channel.

swapping the channels gives the same behaviour...

The drive works quite well (another os on it).

any idea would be welcome.

Thanks a lot.

rmgls
rmgls_at_wanadoo.fr