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
If that doesn't work, then Grub somehow got removed or corrupted. Use Boot Repair to reinstall and fix it.
First, you'll need to boot from a Ubuntu Live CD.
Repair the bootloader
To restore the Grub bootloader, follow these steps.
Open a terminal from the Live CD, and run the following commands:
sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo apt-get update
sudo apt-get install -y boot-repair
After a few seconds, Boot Repair's main window will open.
Reboot to test everything out.
If everything went well, you should be up and running by now.