Pelo live-CD mesmo, tenta o procedimento de recuperação do grub
Pois é, como disse o amigo acima, tente fazer isso:
http://www.vivaolinux.com.br/dica/Como-recuperar-o-GRUB-em-3-comandos-Esse-funciona
Esse comando simplesmente não funciona :
grub-install --root-directory=mnt/dev/sda
install_device not specified.
Usage: grub-install [OPTION] install_device
Install GRUB on your drive.
-h, --help print this message and exit
-v, --version print the version information and exit
--modules=MODULES pre-load specified modules MODULES
--root-directory=DIR install GRUB images under the directory DIR
instead of the root directory
--grub-setup=FILE use FILE as grub-setup
--grub-mkimage=FILE use FILE as grub-mkimage
--grub-probe=FILE use FILE as grub-probe
--no-floppy do not probe any floppy drive
--recheck probe a device map even if it already exists
--force install even if problems are detected
--disk-module=MODULE disk module to use
INSTALL_DEVICE can be a GRUB device name or a system device filename.
grub-install copies GRUB images into /boot/grub (or /grub on NetBSD and
OpenBSD), and uses grub-setup to install grub into the boot sector.
If the --root-directory option is used, then grub-install will copy
images into the operating system installation rooted at that directory.
Report bugs to <bug-grub@gnu.org>.
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Eu olhei dentro do mnt montado e lá não tem nenhum sda, sda1, não tem hd nenhum lá.