Booting the desktop problem
To make along story short, the desktop PC won’t boot.
After some digging around, something must have happened to the BIOS? because all the reference points in the grub menu (/boot/grub/menu.lst) were pointing to (hd0,4).
But it turns out that (hd0,4) is not a partition all of a sudden, and it should be (hd0,3). I’m referring to /dev/sda4 partition.
Anyway, to install the grub menu in the mbr, try this in the grub menu console:
grub> root (hd0,3) #this I think tells grub which partition is root
grub> find /boot/grub/stage1 #this I think tells grub where to get the stage1 data.
grub> setup (hd0) #this I think tells grub where to install itself