That is usually what shows up when there is no bootloader. Looking at the
previous screenshots, I don't think your attempt to install Trisquel was even
successful, as there seems to be no partition on your desired drive or any of
them that could be holding it. That is why, earlier, GRUB gave you the
"Error: no such device." GRUB was fine all along and just couldn't find the
non-existent Trisquel. And I am guessing the grub-repair somehow got rid of
GRUB.
As for why Trisquel didn't actually install, I think it is because the target
drive, that 128GB drive, is almost full, if I am looking at the screenshots
correctly. If you can get some of your data off of it, maybe around 30GB
worth, the automatic "Install alongside Windows" option would probably work
fine.
As for why it LOOKED like it installed successfully and actually didn't...
who knows! In essence, you are back to square one.
