grub2 - Unable to boot: Missing Operating system

I had installed Ubuntu 11.10 along with the another Ubuntu 11.10 which already installed on my netbook. Later I formatted the partition I newly installed. Next time when I boot it went to Grub Rescue menu. I boot my system again with Ubuntu USB stick, Then I installed Boot repair package in USB and restored MBR and GRUB menu in the hard disk. Now when I am restarting, I am getting a message "Missing operating system." press any key to continue.
Can somebody help me on this?

Below is the output for sudo fdisk -l

omitting empty partition (7)

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders, total 312581808 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00058a60


  Device Boot Start End Blocks Id System
/dev/sda1 * 2048 204072287 102035120 83 Linux
/dev/sda2 204072958 312580095 54253569 5 Extended
/dev/sda5 310507520 312580095 1036288 82 Linux swap / Solaris
/dev/sda6 308432896 310503423 1035264 82 Linux swap / Solaris

Partition table entries are not in disk order

Disk /dev/sdb: 4006 MB, 4006608896 bytes

124 heads, 62 sectors/track, 1017 cylinders, total 7825408 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0004d3df

  Device Boot Start End Blocks Id System
/dev/sdb1 * 62 7818695 3909317 b W95 FAT32

Below is the output for sudo blkid

/dev/loop0: TYPE="squashfs" 
/dev/loop1: LABEL="casper-rw" UUID="533defb1-f073-254a-b46f-7ca0ac1f4e0c" TYPE="ext2" 
/dev/sda1: LABEL="Ubuntu" UUID="6a141040-3ba8-457a-9de5-ad06e6057084" TYPE="ext4" 
/dev/sda5: UUID="3a7f62d6-9c65-4d12-a3b6-5d62b9710f7d" TYPE="swap" 
/dev/sda6: UUID="274da115-cec2-4418-a1af-88fe921e3670" TYPE="swap" 
/dev/sdb1: LABEL="PENDRIVE" UUID="EC22-6BE4" TYPE="vfat" 

File /boot/grub/grub.cfg

#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub

#

### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
  set have_grubenv=true
  load_env
fi
set default="0"
if [ "${prev_saved_entry}" ]; then
  set saved_entry="${prev_saved_entry}"

  save_env saved_entry
  set prev_saved_entry=
  save_env prev_saved_entry
  set boot_once=true
fi

function savedefault {
  if [ -z "${boot_once}" ]; then
  saved_entry="${chosen}"
  save_env saved_entry

  fi
}

function recordfail {
  set recordfail=1
  if [ -n "${have_grubenv}" ]; then if [ -z "${boot_once}" ]; then save_env recordfail; fi; fi
}

function load_video {
  insmod vbe

  insmod vga
  insmod video_bochs
  insmod video_cirrus
}

insmod part_msdos
insmod ext2
set root='(hd0,msdos1)'
search --no-floppy --fs-uuid --set=root 6a141040-3ba8-457a-9de5-ad06e6057084
if loadfont /usr/share/grub/unicode.pf2 ; then

  set gfxmode=auto
  load_video
  insmod gfxterm
  insmod part_msdos
  insmod ext2
  set root='(hd0,msdos1)'
  search --no-floppy --fs-uuid --set=root 6a141040-3ba8-457a-9de5-ad06e6057084
  set locale_dir=($root)/boot/grub/locale
  set lang=en_US
  insmod gettext

fi
terminal_output gfxterm
if [ "${recordfail}" = 1 ]; then
  set timeout=10
else
  set timeout=10
fi
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/05_debian_theme ###

set menu_color_normal=white/black
set menu_color_highlight=black/light-gray
if background_color 44,0,30; then
  clear
fi
### END /etc/grub.d/05_debian_theme ###

### BEGIN /etc/grub.d/10_linux ###
if [ ${recordfail} != 1 ]; then
  if [ -e ${prefix}/gfxblacklist.txt ]; then

  if hwmatch ${prefix}/gfxblacklist.txt 3; then
  if [ ${match} = 0 ]; then
  set linux_gfx_mode=keep
  else
  set linux_gfx_mode=text
  fi
  else
  set linux_gfx_mode=text
  fi
  else

  set linux_gfx_mode=keep
  fi
else
  set linux_gfx_mode=text
fi
export linux_gfx_mode
if [ "$linux_gfx_mode" != "text" ]; then load_video; fi
menuentry 'Ubuntu, with Linux 3.0.0-12-generic' --class ubuntu --class gnu-linux --class gnu --class os {
    recordfail
    set gfxpayload=$linux_gfx_mode

    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos1)'
    search --no-floppy --fs-uuid --set=root 6a141040-3ba8-457a-9de5-ad06e6057084
    linux   /boot/vmlinuz-3.0.0-12-generic root=UUID=6a141040-3ba8-457a-9de5-ad06e6057084 ro quiet splash vt.handoff=7
    initrd  /boot/initrd.img-3.0.0-12-generic
}
menuentry 'Ubuntu, with Linux 3.0.0-12-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os {
    recordfail

    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos1)'
    search --no-floppy --fs-uuid --set=root 6a141040-3ba8-457a-9de5-ad06e6057084
    echo    'Loading Linux 3.0.0-12-generic ...'
    linux   /boot/vmlinuz-3.0.0-12-generic root=UUID=6a141040-3ba8-457a-9de5-ad06e6057084 ro recovery nomodeset 
    echo    'Loading initial ramdisk ...'
    initrd  /boot/initrd.img-3.0.0-12-generic
}

### END /etc/grub.d/10_linux ###

### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###

### BEGIN /etc/grub.d/20_memtest86+ ###
menuentry "Memory test (memtest86+)" {
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos1)'

    search --no-floppy --fs-uuid --set=root 6a141040-3ba8-457a-9de5-ad06e6057084
    linux16 /boot/memtest86+.bin
}
menuentry "Memory test (memtest86+, serial console 115200)" {
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos1)'
    search --no-floppy --fs-uuid --set=root 6a141040-3ba8-457a-9de5-ad06e6057084
    linux16 /boot/memtest86+.bin console=ttyS0,115200n8
}

### END /etc/grub.d/20_memtest86+ ###

### BEGIN /etc/grub.d/30_os-prober ###
### END /etc/grub.d/30_os-prober ###

### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###


### BEGIN /etc/grub.d/41_custom ###
if [ -f $prefix/custom.cfg ]; then
  source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###

Your Grub file seems ok. I suggest installing Grub2 manually again. First, start Ubuntu from USB stick and do not mount your installed Ubuntu. Open a terminal and apply those commands:

sudo mount /dev/sda1 /mnt
sudo mount --bind /dev /mnt/dev
sudo mount --bind /dev/pts  /mnt/dev/pts
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys  /mnt/sys
sudo chroot /mnt
grub-install --force /dev/sda

You can check if it is OK or not with:

grub-install --recheck --force /dev/sda

If everything is ok, unmount all the things and quit:

exit
sudo umount /mnt/dev/pts
sudo umount /mnt/dev
sudo umount /mnt/proc

sudo umount /mnt/sys
sudo umount /mnt
sudo reboot