Problem with booting freebsd

[Adil F. Mamedov]

Hello!

After my WINDOWS XP crashed, I decided to reinstall it... But I forgot
that during windows installation it overwrites the MBR. So, instead of
prompting me for the OS to load (FreeBSD or Windows), the system loads
Windows. When I found this problem, I have booted my system from the CD,
then entered Fixit menu, booted the Live File System CD and went to the
Console at VTY4. Then I did the following:

 

mount /dev/ad0s3a /mnt   -   mount root filesystem

fdisk -B -b /mnt/boot/boot0 /dev/ad0   -   recover the MBR

 

The last command gives me the error: ad0 Permission Denied.

Note, that my Live File System CD is for the 4.4 Release, but I have 5.3
Release installed on my system. I don't expect this to be the reason of
my problem, but anyway, who knows ....