/boot/loader Invalid Format

[Webmaster Shizukana.net]

Can somebody help me?

I've got a problem with my bootloader and i dont know how to fix it.
If I boot my pc, it stops loading, it says:

Invalid Format.

FreeBSD/i386-Release 5.3
default: 0:ad(0,a)/kernel
boot:

and it is in the /boot/loader
how can i fix this?
is there a disk to boot to prompt, so i can mount the / of my freebsd
system and update the /boot/loader file with the one of someone else?

and ifso, how can i do this with the mount commands?

thanks!
Nexohrion