I had an "old" unused Toshiba Satellite M50D-A at my place (it didn't have any OS installed anymore), so I decided to put Ubuntu 16.04.3 LTS on a USB and give it a try. It might be worth noting that I'm entirely new at these things and I have little to zero IT knowledge as well.
Anyway, this is what I did (remember Windows was already erased before I started doing this):
1) Downloaded Ubuntu 16.04.3 LTS 64-bit
2) Used Rufus to create a bootable USB
3) Plugged it into my laptop and went for "Try Ubuntu" in GRUB
4) Installed Ubuntu through the live session
After a successful install, however, Ubuntu doesn't want to boot (unless I plug in the USB again which gives me the same options again as in the beginning - Try Ubuntu, Install Ubuntu, etc).
The following error pops up for about 2 seconds:
Failed to open \EFI\BOOT\mmx64.efi - Not Found
Failed to load image \EFI\BOOT\mmx64.effi: Not Found
Failed to start MokManager: Not Found
Failed to open \EFI\BOOT\grubx64.efi - Not Found
Failed to load image \EFI\BOOT\grubx64.efi: Not Found
start_image() returned Not Found
Followed immediately by:
Reboot and select proper Boot device
or Insert Boot Media in selected Boot device and press a key
After booting a live session through USB again, I followed some steps to install Boot Repair. The recommended repair didn't change anything, unfortunately. Here's my pastebin: https://paste.ubuntu.com/26401439/
I also disabled Secure Boot, and the Boot Mode is set to UEFI.
I hope someone is able to help!