Switch to root using ‘su’ command and execute ‘grub’ command in terminal/konsole. Prompt will change to ‘grub>’
execute md5crypt to generate password hash.

grub> md5crypt

it will prompt you for password, enter the password which you are going to set for GRUB. it will display encrypted password hash.

Password: *******
Encrypted: $1$X2jZi$KeCC6NuRp0BJDt32jCvnw0

note down encrypted password hash or copy it and exit grub mode using the grub command.

grub> quit

Now edit the
edit /boot/grub/menu.lst file and insert encrypted password above the “title” lines or insert near commented examples of password line.

password –md5 <password-hash>
## ## End Default Options ##
title        Ubuntu 8.04.1, kernel 2.6.24-19-generic

save edited file and reboot.

This is because, Windows in not more friendly. When you install the Windows it over writes other Boot loaders with its own. Also doesnot identify other Operating systems in the hard drive. Where are opend source boot loaders such as GRUB that come with most of the linus distros are more friendly and detects amost all operating systems.

So to get back your Ubuntu. Just install GRUB (Boot Loader) alone with the help of a Ubuntu cd or dvd, that will take few second than wasting you precious time. Also will give you back the same Ubuntu that you were using before and all softwares install as before….

To install GRUB alone follow the steps:

1. Boot your system with a Ubuntu Bootable Cd and Choose Live CD mode

2. After the Ubuntu boots in the Live-CD mode, press Alt-F2 and type gnome-terminal, and press Enter

3. Now follow the commands below

sudo grub
find /boot/grub/stage1
root (x,y)
setup (x)
quit
sudo shutdown “now” -r

The resulting “find” command will display something like (hd0,1). In this example, you would then type root (hd0,1) and then setup (hd0) in the above area. These numbers might be different; that’s why I included the “find” command. So that find command will locate the partition where linux wass installed previously. That is Ubuntu partitions located either in front or behind their Windows installation or on a completely separate internal/external hard