grub2 not booting after changes to grub file

I am using Ubuntu 16.04. Single OS boot. After implementing the instructions given in https://askubuntu.com/a/362998 to rectify Ubuntu logo appearance during grub boot loading, I find my system unable to boot. It is stalled in a purple screen after grub2 menu stage.

I have gone through the instructions of this website to manually boot up from grub but nothing happens after I issued the boot command.

How do I get grub to correctly boot my system in grub?

How do I correct the /etc/default/grub file, example to return it to the original state and perform update-grub and update-initramfs at grub prompt?

You have a lot of questions in there. I can address this one of them:

How do I correct the /etc/default/grub file?

Boot into live USB

Mount the ubuntu partition drive sudo mount /dev/sda1 /mnt

Mount the virtual filesystems:

        sudo mount --bind /dev /mnt/dev
        sudo mount --bind /proc /mnt/proc 
        sudo mount --bind /sys /mnt/sys

To ensure that only the grub utilities from the LiveCD get executed, mount /usr

       sudo mount --bind /usr /mnt/usr 
       sudo chroot /mnt  

Make your changes to /etc/default/grub using nano

run the updater update-grub

Exit chroot : CTRL-D on keyboard.

Unmount virtual filesystems:

       sudo umount /mnt/dev 
       sudo umount /mnt/proc
       sudo umount /mnt/sys 
       sudo umount /mnt/usr
       sudo umount /mnt

sudo reboot

Source: Sadly can't remember where I found this, but it worked, so I copied it and saved it.