This question already has an answer here:
A few hours ago, I went in my ACER laptop boot options, for no particular reason. I did not change anything, but noticed that Windows 10 was first in the boot order list while Ubuntu was not there at all. I escaped, and thought Grub would show up... but it did not and Windows booted.
Since then, I've been unable to boot on Ubuntu. Windows automatically boots and Grub does not show up anymore.
In the boot menu, there is only Windows. I'm on UEFI and secure boot is enabled - it wont let me disabled it in the options.
Prior to that, everything used to work just fine. I'm confused!
- EDIT : Problem fixed, see my answer.