I am trying to install another linux distro besides ubuntu. However, I want to retain my existing windows based loader. Currently, as per my knowledge, MsDos loads grub which then loads Ubuntu (with loop back trick).
Now, I have a new linux distro installed on /dev/sda8 (/boot for new distro) where as /root for that OS is installed on /dev/sda9. 
I tried following steps
1. Add entry into 40_custom of ubuntu grub
2. update grub
But upon booting via that entry, it is not able to load the new OS and shows me blank screen. What could be the problem?
Additional data:
grub.cfg file of ubuntu
menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-fc296be2-8c59-4f21-a3f8-47c38cd0d537' {
  gfxmode $linux_gfx_mode
  insmod gzio
  insmod ntfs
  set root='hd0,msdos5'
  if [ x$feature_platform_search_hint = xy ]; then
    search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos5 --hint-efi=hd0,msdos5 --hint-baremetal=ahci0,msdos5  01CD7BB998DB0870
  else
    search --no-floppy --fs-uuid --set=root 01CD7BB998DB0870
  fi
  loopback loop0 /ubuntu/disks/root.disk
  set root=(loop0)
  linux   /boot/vmlinuz-3.5.0-19-generic root=UUID=01CD7BB998DB0870 loop=/ubuntu/disks/root.disk ro   quiet splash $vt_handoff
  initrd  /boot/initrd.img-3.5.0-19-generic
}
submenu 'Advanced options for Ubuntu' $menuentry_id_option 'gnulinux-advanced-fc296be2-8c59-4f21-a3f8-47c38cd0d537' {
  menuentry 'Ubuntu, with Linux 3.5.0-19-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.5.0-19-generic-advanced-fc296be2-8c59-4f21-a3f8-47c38cd0d537'     {
      gfxmode $linux_gfx_mode
      insmod gzio
      insmod ntfs
      set root='hd0,msdos5'
      if [ x$feature_platform_search_hint = xy ]; then
        search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos5 --hint-efi=hd0,msdos5 --hint-baremetal=ahci0,msdos5  01CD7BB998DB0870
      else
        search --no-floppy --fs-uuid --set=root 01CD7BB998DB0870
      fi
      loopback loop0 /ubuntu/disks/root.disk
      set root=(loop0)
      echo    'Loading Linux 3.5.0-19-generic ...'
      linux   /boot/vmlinuz-3.5.0-19-generic root=UUID=01CD7BB998DB0870 loop=/ubuntu/disks/root.disk ro   quiet splash $vt_handoff
      echo    'Loading initial ramdisk ...'
      initrd  /boot/initrd.img-3.5.0-19-generic
  }
  menuentry 'Ubuntu, with Linux 3.5.0-19-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.5.0-19-generic-recovery-fc296be2-8c59-4f21-a3f8-47c38cd0d537' {
      insmod gzio
      insmod ntfs
      set root='hd0,msdos5'
      if [ x$feature_platform_search_hint = xy ]; then
        search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos5 --hint-efi=hd0,msdos5 --hint-baremetal=ahci0,msdos5  01CD7BB998DB0870
      else
        search --no-floppy --fs-uuid --set=root 01CD7BB998DB0870
      fi
      loopback loop0 /ubuntu/disks/root.disk
      set root=(loop0)
      echo    'Loading Linux 3.5.0-19-generic ...'
      linux   /boot/vmlinuz-3.5.0-19-generic root=UUID=01CD7BB998DB0870 loop=/ubuntu/disks/root.disk ro recovery nomodeset 
      echo    'Loading initial ramdisk ...'
      initrd  /boot/initrd.img-3.5.0-19-generic
  }
}
### END /etc/grub.d/10_lupin ###
menuentry 'Linux, with Linux core repo kernel' --class arch --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-core repo kernel-true-0f490b6c-e92d-42f0-88e1-0bd3c0d27641'{
  load_video
  set gfxpayload=keep
  insmod gzio
  insmod part_msdos
  insmod ext2
  set root='hd0,msdos8'
  if [ x$feature_platform_search_hint = xy ]; then
    search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos8 --hint-efi=hd0,msdos8 --hint-baremetal=ahci0,msdos8  0f490b6c-e92d-42f0-88e1-0bd3c0d27641
  else
    search --no-floppy --fs-uuid --set=root 0f490b6c-e92d-42f0-88e1-0bd3c0d27641
  fi
  echo  'Loading Linux core repo kernel ...'
  linux /boot/vmlinuz-linux root=UUID=0f490b6c-e92d-42f0-88e1-0bd3c0d27641 ro  quiet
  echo  'Loading initial ramdisk ...'
  initrd  /boot/initramfs-linux.img
}
menuentry 'Linux, with Linux core repo kernel (Fallback initramfs)' --class arch --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-core repo kernel-fallback-0f490b6c-e92d-42f0-88e1-0bd3c0d27641' {
  load_video
  set gfxpayload=keep
  insmod gzio
  insmod part_msdos
  insmod ext2
  set root='hd0,msdos8'
  if [ x$feature_platform_search_hint = xy ]; then
    search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos8 --hint-efi=hd0,msdos8 --hint-baremetal=ahci0,msdos8  0f490b6c-e92d-42f0-88e1-0bd3c0d27641
  else
    search --no-floppy --fs-uuid --set=root 0f490b6c-e92d-42f0-88e1-0bd3c0d27641
  fi
  echo  'Loading Linux core repo kernel ...'
  linux /boot/vmlinuz-linux root=UUID=0f490b6c-e92d-42f0-88e1-0bd3c0d27641 ro  quiet
  echo  'Loading initial ramdisk ...'
  initrd  /boot/initramfs-linux-fallback.img
}
lsblk
NAME    MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda       8:0    0 931.5G  0 disk 
+-sda1    8:1    0  39.2M  0 part 
+-sda2    8:2    0  19.8G  0 part 
+-sda3    8:3    0 205.1G  0 part 
+-sda4    8:4    0     1K  0 part 
+-sda5    8:5    0 333.7G  0 part /host
+-sda6    8:6    0 233.4G  0 part 
+-sda7    8:7    0 100.4G  0 part 
+-sda8    8:8    0   100M  0 part 
+-sda9    8:9    0  14.7G  0 part 
+-sda10   8:10   0  21.4G  0 part 
+-sda11   8:11   0     3G  0 part 
sr0      11:0    1  1024M  0 rom  
loop0     7:0    0    29G  0 loop /
blkid
/dev/loop0: UUID="fc296be2-8c59-4f21-a3f8-47c38cd0d537" TYPE="ext4" 
/dev/sda1: SEC_TYPE="msdos" LABEL="DellUtility" UUID="5450-4444" TYPE="vfat" 
/dev/sda2: LABEL="RECOVERY" UUID="78C4FAC1C4FA80A4" TYPE="ntfs" 
/dev/sda3: LABEL="OS" UUID="DACEFCF1CEFCC6B3" TYPE="ntfs" 
/dev/sda5: UUID="01CD7BB998DB0870" TYPE="ntfs" 
/dev/sda6: UUID="01CD7BB99CA3F750" TYPE="ntfs" 
/dev/sda7: LABEL="Windows 8" UUID="01CDBFB52F925F40" TYPE="ntfs" 
/dev/sda8: UUID="cdbb5770-d29c-401d-850d-ee30a048ca5e" TYPE="ext2" 
/dev/sda9: UUID="0f490b6c-e92d-42f0-88e1-0bd3c0d27641" TYPE="ext2" 
/dev/sda10: UUID="2e7682e5-8917-4edc-9bf9-044fea2ad738" TYPE="ext2" 
/dev/sda11: UUID="6081da70-d622-42b9-b489-309f922b284e" TYPE="swap
Any help is appreciated. Please let me know if you need any extra data.