Problems trying to install Ubuntu 18.10 in Aspire A515-51

Comecacahuates

I just bought a new Aspire A515-51, and I tried to install Ubuntu 18.10 but I'm having trouble. I pressed F2 to enter the BIOS and enable the boot menu, and I created a live USB following these instructions. I was able to run Ubuntu from the USB, but it didn't show the dev/sda when I had to select the partition to install it. I tried disabling UEFI, but it was the same, so I enabled it again. I don't remember if I did anything else after that, but when I tried to run Ubuntu from the USB again, after I select the USB in the boot menu, it shows a message that says the following:

Failed to open \EFI\BOOT\mmx64.efi - Not Found

Failed to load image \EFI\BOOT\mmx64.efi: Not Found

Failed to start MokManager: Not Found

Something has gone seriously wrong: import_mok_state() failed

: Not Found

And then it shuts down.

Is there something I can do to be able to install it?

Comecacahuates

I solved the booting problem renaming the file grubx64.efi to mmx64.efi, but I still have the problem with the installation: it doesn't show the /dev/sda.