[RootbeaR]

"I like to have lots of choice about which operating system I can boot to. Between my desktop PC’s two hard drives, I have at least three distributions of Linux and several versions of Windows, so I have complete OS flexibility.

Unfortunately, maintaining a multi-boot configuration like this can be a pain, especially if you later install an operating system which overwrites the GRUB boot loader you had in place (such as a version of Windows). If your boot loader is overwritten, you could be left with no choice but to boot the most recently installed OS.

In this tutorial, I will show you how to restore an overwritten copy of the GRUB boot loader by using a Linux live CD. In this example, my master GRUB installation is on a Kubuntu 8.10 installation, and I’m using an older Kubuntu 8.04 Live CD I have lying around."
http://fosswire.com/post/2009/5/rest...rwritten-grub/

[saikee]

Many Live CD now use stage2_eltorito instead of isolinux for booting. That means Grub is available before a Linux is booted

Press "esc" follow by the "c" key can drop a user into a Grub prompt.

In a Grub prompt one can see the partition layout of the 1st and 2nd disk by

geometry (hd0)
geometry (hd1)

If one want restore Grub in partition (hd0,2) to MBR the commands are

root (hd0,2)
setup (hd0)

To make the partition (hd0,2) chainloadable by another boot loader the command is

root (hd0,2)
setup (hd0,2))

Any installed Dos, Windows, Vista must have a ntfs partition of Type 7, say it is in (hd0,0) then Grub can fire it up by command

root (hd0,0)
makeactive
chainloader +1
boot

With a bit of experience a Grub prompt is all a PC user needs to boot any installed OS. A Linux can have no boot loader installed yet it can be booted manually by a Grub prompt.