Here are the details of my installation :
My computer is this one : https://www.acer.com/datasheets/2016/48 ... F.002.html. I turned off fast-boot in the control panel, then rebooted my computer, accessed the BIOS and disabled secure boot. I booted from a debian net-install DVD, and I followed through the graphical installation. There was firmware which was missing, but from what I can tell it's wi-fi configuration firmware so it shouldn't have anything to do with my problem. Aside from that, the installation went fine. I installed the system on a partition of the computer's second disk.
When my computer restarted after the installation, it launched windows directly. The BIOS doesn't show any system to be booted other than windows. I booted debian on a live CD and used chroot to access my debian installation, which worked fine. I then followed these instructions : https://wiki.debian.org/GrubEFIReinstall to run a grub-install command (I told it to use sda1 as the boot partition). I also followed the instructions for getting the correct fallback bootloader :
It's possible that I did something wrong during that process, because I was following multiple tutorials and not entirely sure of what I was doing, but it seems to me like everything works. In the end, I rebooted the computer and nothing had improved.cp debian/grubx64.efi boot/bootx64.efi
I don't really know what's going on, if anyone can explain this to me or tell me how to fix it that would be great.