Enter in to the single use mode.
ok boot cdrom –s
# mount /dev/dsk/c0t0d0s0 /a
# cd /a/etc
# TERM = vt100
# export TERM
# vi shadow
Here, remove the roots encrypted password string then save and exit.
# cd/
# umount /a
# init6
This will restart the system and now the root login can be entered without password.   _{Your Comment}