ubuntu installed, but not booting

please load into ubuntu via recovery, and login. Open a terminal by clicking 'Applications' at the top-left of the screen, then accessories, then terminal.

enter these commands one at a time!

cd /boot/grub
cat menu.lst > ~/mygrub.txt
cd ~
gedit mygrub.txt

this should load up a text editor with your grub configuration. Please paste it all here. So I can examine it.

this is the details in mygrub.txt

# menu.lst - See: grub(8), info grub, update-grub(8)
# grub-install(8), grub-floppy(8),
# grub-md5-crypt, /usr/share/doc/grub
# and /usr/share/doc/grub-doc/.

## default num
# Set the default entry to the entry number NUM. Numbering starts from 0, and
# the entry number 0 is the default if the command is not used.
#
# You can specify 'saved' instead of a number. In this case, the default entry
# is the entry saved with the command 'savedefault'.
# WARNING: If you are using dmraid do not change this entry to 'saved' or your
# array will desync and will not let you boot your system.
default 0

## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout 10

## hiddenmenu
# Hides the menu by default (press ESC to see the menu)
#hiddenmenu

# Pretty colours
#color cyan/blue white/blue

## password ['--md5'] passwd
# If used in the first section of a menu file, disable all interactive editing
# control (menu entry editor and command-line) and entries protected by the
# command 'lock'
# e.g. password topsecret
# password --md5 $1$gLhU0/$aW78kHK1QfV3P2b2znUoe/
# password topsecret

#
# examples
#
# title Windows 95/98/NT/2000
# root (hd0,0)
# makeactive
# chainloader +1
#
# title Linux
# root (hd0,1)
# kernel /vmlinuz root=/dev/hda2 ro
#

#
# Put static boot stanzas before and/or after AUTOMAGIC KERNEL LIST

### BEGIN AUTOMAGIC KERNELS LIST
## lines between the AUTOMAGIC KERNELS LIST markers will be modified
## by the debian update-grub script except for the default options below

## DO NOT UNCOMMENT THEM, Just edit them to your needs

## ## Start Default Options ##
## default kernel options
## default kernel options for automagic boot options
## If you want special options for specific kernels use kopt_x_y_z
## where x.y.z is kernel version. Minor versions can be omitted.
## e.g. kopt=root=/dev/hda1 ro
## kopt_2_6_8=root=/dev/hdc1 ro
## kopt_2_6_8_2_686=root=/dev/hdc2 ro
# kopt=root=UUID=8c1bfd35-dab4-4eac-b51c-9077a3ba8690 ro

## Setup crashdump menu entries
## e.g. crashdump=1
# crashdump=0

## default grub root device
## e.g. groot=(hd0,0)
# groot=(hd0,2)

## should update-grub create alternative automagic boot options
## e.g. alternative=true
## alternative=false
# alternative=true

## should update-grub lock alternative automagic boot options
## e.g. lockalternative=true
## lockalternative=false
# lockalternative=false

## additional options to use with the default boot option, but not with the
## alternatives
## e.g. defoptions=vga=791 resume=/dev/hda5
# defoptions=quiet splash

## should update-grub lock old automagic boot options
## e.g. lockold=false
## lockold=true
# lockold=false

## Xen hypervisor options to use with the default Xen boot option
# xenhopt=

## Xen Linux kernel options to use with the default Xen boot option
# xenkopt=console=tty0

## altoption boot targets option
## multiple altoptions lines are allowed
## e.g. altoptions=(extra menu suffix) extra boot options
## altoptions=(recovery) single
# altoptions=(recovery mode) single

## controls how many kernels should be put into the menu.lst
## only counts the first occurence of a kernel, not the
## alternative kernel options
## e.g. howmany=all
## howmany=7
# howmany=all

## should update-grub create memtest86 boot option
## e.g. memtest86=true
## memtest86=false
# memtest86=true

## should update-grub adjust the value of the default booted system
## can be true or false
# updatedefaultentry=false

## ## End Default Options ##

title Ubuntu, kernel 2.6.20-15-generic
root (hd0,2)
kernel /boot/vmlinuz-2.6.20-15-generic root=UUID=8c1bfd35-dab4-4eac-b51c-9077a3ba8690 ro quiet splash
initrd /boot/initrd.img-2.6.20-15-generic
quiet
savedefault

title Ubuntu, kernel 2.6.20-15-generic (recovery mode)
root (hd0,2)
kernel /boot/vmlinuz-2.6.20-15-generic root=UUID=8c1bfd35-dab4-4eac-b51c-9077a3ba8690 ro single
initrd /boot/initrd.img-2.6.20-15-generic

title Ubuntu, memtest86+
root (hd0,2)
kernel /boot/memtest86+.bin
quiet

### END DEBIAN AUTOMAGIC KERNELS LIST

# This is a divider, added to separate the menu items below from the Debian
# ones.
title Other operating systems:
root

# This entry automatically added by the Debian installer for a non-linux OS
# on /dev/sda1
title Microsoft Windows XP Professional
root (hd0,0)
savedefault
makeactive
chainloader +1

hey Antonio, Thanks, that solved my probelm,
I modified the /boot/grub/menu.lst as you said. Now ubuntu is perfectly being boot up. Though Windows is still having the problem, but that I will manage through XP cd. Now since ubuntu is on, who cares about windows.?

Thanks alot.
also thanks am for your support

Warm Regards
Prasad

Well, the windows problem is rare.
Can you post the result of this command?
sudo fdisk -l /dev/sda

Yes.. OK ... Paste op of sudo fdisk -l /dev/sda let me see.... and dont worry we ll support you!!!!

Yhanks guys
the result of the command is

prasad@Prasad:~$ sudo fdisk -l /dev/sda

Disk /dev/sda: 40.0 GB, 40060403712 bytes
255 heads, 63 sectors/track, 4870 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot Start End Blocks Id System
/dev/sda1 * 1 1275 10241406 c W95 FAT32 (LBA)
/dev/sda2 1276 1288 104422+ 83 Linux
/dev/sda3 1289 4384 24868620 83 Linux
/dev/sda4 4385 4870 3903795 82 Linux swap / Solaris

Thanks again
Prasad

OK You have two linux partitions and win xp on sda1.. Now windows isnt starting... Thats the problem right?