So here is the problem. I have a packard bell desktop that had windows 8 installed but not really working. Long story short: I was installing xubuntu 18.04 when electricity went down.
When I was able to turn on the computer, this error showed up. I found some info online about the fact that I needed the mmx64.efi file hence I downloaded the latest version of xubuntu, i.e. 19.10, that has it. I used etcher to put the iso into a working USB and then I started the installation again.
Now it has been 24 hours of something. The installation is not stuck since the terminal from the installation window is sending messages but still I believe something is wrong.
I found this tutorial but I am unsure of what to do now. Should I restart the installation or should I wait? Any clues?
EDIT: I forgot to mention that I wanted a fresh install, so I choose to let xubuntu erase the disk and partition it accordingly to its needs.