If so then I do not think wiping out the disk can help.
Because I tried to install standard NetBSD boot loader which as far as I
know erase MBR sector.
Moreover, I also used FreeBSD installer which can zero MBR here I did not
install NBSD boot loader. But, both of these way could not help me.

2007/2/28, Stephen Borrill <netbsd@precedence.co.uk>:
>
> On Wed, 28 Feb 2007, Alexander Bubnov wrote:
> >> Maybe try zapping the disk with
> >>
> >>   dd if=/dev/zero of=/dev/rwd0d count=100
> >>
> >> and try again with option b ?
> >
> > Thanks for help!
> >
> > One more question before the next trial.
> > What does this command do? Does it check a disk for bad sectors?
>
> No, it wipes out the fdisk partition table, boot code and NetBSD disklabel
> (if the NetBSD partition is at the beginning of the disk).
>
> I'm not sure that option b will work though as there won't be any
> partition to reinstall onto.
>
> --
> Stephen