I have used mfsBDS CD, http://mfsbsd.vx.sk/
, to boot the laptop and login as root, password mfsroot.
Mounted the boot partition:
mfsbsd# mount /dev/label/boot0 /mnt
I have lost the /boot/loadeer.conf file, but fortunately I have a copy named loader.conf.orig.
mfsbsd# cp /mnt/boot/loader.conf.orig /mnt/boot/loader.conf
and rebooted the system
mfsbsd# shutdown -r now
Now all works.
I have done a backup copy of the /boot directory in my home directory.
Booting with the mfsBSD CD, the command:
mfsbsd# zpool import tank0
will mounts the HD tank0/usr in /usr and tank0/var in /var directory.
And the command
#mount /dev/label/boot0 /mnt
mounts the HD boot partition.
Doing so I can restore the boot partition from the copy in my home directory.