Try to show the Grub menu
Hold down the
Shift key as the computer attempts to boot to display the GRUB 2
menu. In certain circumstances, if holding the Shift key method does
not display the menu pressing the Esc key repeatedly may display the
menu.
If that doesn't work, then using Boot Repair to reinstall and fix Grub.
Boot Repair
Repair the bootloader
To restore the Grub bootloader, follow these steps.
Open a terminal, and run the following commands:
sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo apt-get update
sudo apt-get install -y boot-repair
boot-repair
After a few seconds, Boot Repair's main window will open.
Click on Recommended repair
.
You're done!
Reboot to test everything out.
If everything went well, you should be up and running by now.
Glossary
Bootloader: a piece of code that runs before any operating system is running. A bootloader is used to boot other operating
systems. Each operating system usually has its own bootloader.
GRUB (Grand Unified Bootloader): a bootloader package developed to support multiple operating systems and allow the user to select among them during boot-up. It is Ubuntu's default bootloader.
Command, command line: the traditional Unix environment , where you type commands to tell the computer what to do.
Terminal: an application that allows you to access the command line. Open it by hitting its keyboard shortcut, Ctrl Alt T