Hi again, @NilleB 
You wrote:
Hmmm.... Given that you are able to boot via recovery mode, my suggestion is to boot in that recovery mode and REMOVE the "quiet" and "splash" options from the default Linux Kernel option in the GNU GRUB (GRand Unified Boot Loader) configuration.
To do that, please edit the /etc/default/grub file with administrator privileges, by running the following command (that will open the "Pluma" text editor as superuser):
sudo pluma /etc/default/grub
In that /etc/default/grub file, change the following line
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
... change that line so it becomes the following one instead:
GRUB_CMDLINE_LINUX_DEFAULT=""
(To explain a bit what this does: removing "quiet" from the boot options allows the boot messages to appear and removing "splash" disables the so-called splash screen).
After doing that, please save and close that /etc/default/grub file, and then run the following command:
sudo update-grub
After running that sudo update-grub command, please reboot the computer and see if the following boot is normal. IF that boot is NOT normal, I'll assume that you will then be able to see error messages on screen and, in that case, could you please take a photo of those error messages using, for instance, the camera of your smartphone and include it a new reply in this same discussion topic?
I make this suggestion (of removing "quiet splash" from the boot options of GRUB) because I like to see the boot messages while booting and also because this seems to have helped other people, here in the "Ubuntu MATE Community", in different contexts. See, for instance, the following replies of mine in different topics:
I hope this helps Please, keep us posted!