Recently we got a mail from one of readers who is not able to boot from Linux on his computer after he had installed Windows XP.There was Linux already installed on his computer.
All this has actually occurred because of wrong order of install of these operating system.
It is always desired that you install windows before you install Linux as the installation other way round would result in corrupted boot-loader and you will not get the option to boot from Linux.
Due to wrong sequence of installation of windows over a Linux system, windows erases the existing boot-loader from boot sector of the hard disk. It overwrites existing boot sector with the windows boot-loader (NTLDR).
But don’t worry as you can simply fix this using a Linux bootable CD /DVD.
Boot the computer with the Linux bootable CD / DVD.
1. At the boot prompt, type ‘linux rescue‘ (without quotes) and hit enter.
2. Continue with the default options through the prompts.
3. When you get to a bash prompt, type ‘chroot /mnt/sysimage’ (I think that’s the path).
4. Then, type ‘/sbin/grub-install /dev/hda’ (assuming, hda is your system drive).
5. Eject the cd /dvd and reboot your computer ,you will see the default grub bootloader which allows you to boot both with windows and Linux
Hope this info fixes up the trouble.