I built FreeBSD 9.2 within KVM and I can not login as root.
I am not sure if I configured the root password when installing the OS..
Here is how to change root password.
log in as single user mode ( when booting, press 2 )
# fsck –p
# mount –u /
# mount –a
configure the password.
reboot the OS.
To allow users to become the root, edit /etc/group file.
add users in the wheel group.
# cat /etc/group