I had ubuntu14.04LTS running and installed ubuntu 17.04 making a partition. So I got 2 choices at startup. This worked fine until a couple of weeks. I assume after a 14.04 update, the initial menu (grub?) disapeared, and notebook starts directly on 14.04.
I tryed boot-repair with this result: GPT detected. Please create a BIOS-Boot partition (>1MB, unformatted filesystem, bios_grub flag). This can be performed via tools such as Gparted. Then try again. Alternatively, you can retry after activating the [Separate /boot/efi partition:] option.
Things from there are too complicated in forums, I am not an expert, just a user.
Partitions are still there with all the content.
bootinfo from boot-repair: http://paste.ubuntu.com/25575784/
Hope someone can help. Thanks.