Here is my situation. I originally (only) have Ubuntu 14.04 on my laptop. Then, I installed Windows 10 into a free partition. Now, even though Ubuntu's partitions remained, I'm not able to enter Ubuntu when booting. I'm expecting this to happen when I was installing Windows 10, but I don't know how to add the existing Ubuntu to boot menu to fix it. It's fine for me either the boot menu is GRUB or Windows.
Any help is sincerely appreciated!
sudo parted -l
If both are in same boot mode:sudo update-grub
will add Windows to grub menu. – oldfred Jul 14 '16 at 21:54