This tutorial is meant to help you install fix your grub config file, and by doing so enabling you to boot into your right partitions.
Name-codes used in this tutorial:
USERNAME = your username (ex. john, abby,..)
PASSWORD = your password (ex. pAsSwRd123)
DISKNAME = your disk name (ex. sda, hdb, sdc, etc)
PARTITION = your partition name (ex. sda1, sdb2, hda3,..)
#this is a comment = do not type senteces starting with '#'. This is to explain/comment the command
Method #1 – LIVE CD/DVD
1- Boot the computer from an USB or CD ubuntu image. At the boot screen select “Try out”UBUNTU”
2- After the desktop session has loaded start the terminal or just press CTRL+ALT+t
3- At the terminal type:
#now here is the hard part; you have to figure out what is the partition you need to use in the next command, where is your "/" root-linux-system located?
mount /dev/PARTITION /mnt/new #mount the partition where you "/"(root-system) folder is located
grub-install --root-directory=/mnt/new /dev/DISKNAME #install the bootloader in the right disk
4- Now close the terminal, exit the live session, take out the cd and reboot your system.
5- Press “SHIFT” to load the new grub menu, and select “Recovery Mode”
6- In recovery mode , select “UPDATE-GRUB bootloader” and select “OK”;
7- Exit and reboot normally; You should see that the grub menu has changed (in case you had other OS installed in your machine)