Finally, I have found the solution. But the solution doesn't explain why I have been facing this dual boot issue. But I have found no where that these steps that I am going to explain below, are mentioned any where.
Following steps were performed by me:
Step 1: Installed Windows 7.
Please note that I had 3 partitions after Step 1.
/dev/sda -> /dev/sda1 : Windows auto-created 100 MB System reserved partition. -> /dev/sda2 : C Drive. -> /dev/sda2 : D Drive. -> 100 GB Unallocated partition.
Step 2: Created bootable USB of Ubuntu and started live session of Ubuntu.
Step 3: Ran "GParted" and created fourth partition as "Extended Partition". Then I created 2 other logical partitions under the extended partition of 80 GB ( /dev/sda5
) and 20 GB ( /dev/sda6
) respectively.
Step 4: Ran Ubuntu installation and I choose "Something else" to create my own partition scheme for Ubuntu.
Step 5: Re-formatted /dev/sda5 as root partition and /dev/sda6 as swap partition.
Step 6: Selected /dev/sda5 and clicked "next" to continue with the Ubuntu installation.
Step 7: After installation was finished and my laptop had rebooted, I found that my laptop straight entered into Ubuntu. Later, after restarting again, I triggered to show GRUB menu. I found that GRUB menu had no entry for Windows.
Step 8: On the same GRUB menu screen, there was an another option as:
Advanced Options for Ubuntu
.
It led me to an another menu having two options. The second was:
Ubuntu, with Linux 3.16.0-23-generic (recovery mode)
.
Later, it led me to the Recovery Menu
. This menu had several options such as "resume, clean, dpkg, failsafeX, fsck, grub, network, root, system-memory". I chose grub
and hit OK
.
This repaired GRUB and asked me to restart my laptop. Later, when I restarted my laptop and triggered GRUB menu by hitting UP arrow key, and guess what I found. I found that GRUB menu had several options, including "Windows 7".
Then, I tested Ubuntu as well as Windows 7 one by one, and both of them started without any glitch.