Following an installation, from CD, where I selected the option to update the 
MBR,  the computer won't boot and displays an Operating System Not Found 
message.

fdisk -v sd0 shows:

0: NetBSD (sysid 169)
    start 12, size 71687360 (35004 MB, Cyls 0/1/5-746743/5/4), Active
        beg: cylinder    0, head   1, sector  1
        end: cylinder 1023, head  11, sector  8
        PBR is not bootable: Bad magic number (0x0000)>

Running :

installboot -v /dev/rsd0d /boot/bootxx_ffsv1

The computer was running NetBSD prior to the re-installation.

Suggestions?
-- 
John R. Shannon