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:

1. 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
   }
   

2. 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 /

1. 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.