Grub2 install problems

Hi,
I had a dual boot of Fedora 18 and Windows 7. Upgraded windows 7 to Windows 8. But then the grub got corrupted. While manually trying to reinstall grub2 from live usb using the following commands I had a couple of issues:

chroot /mnt/sysimage
grub2-install /dev/sda
grub2-mkconfig -o /boot/grub2/grub.cfg

First issue was that /mnt/sysimage was not there. Second, when trying to install grub with the command "grub2-install /dev/sda" gave error. Please help, need to urgently install the grub since lot of data are in my Fedora login.

Thanks!