Can't get into my Mate desktop (2)

This is a separate thread to the previous of a similar name
For me it became a nightmare. On an Acer S5 (named Aspire S13).

I did the upgrade from 17.10 to 18.04 LTS on the SSD usb attached and still running Win10 on the hard drive, as a back-up, and with a reduced size. Been running 17.10 smoothly since it was out.

After the upgrade, everything was alive on the SSD since I could see and access by using my UM flashdisk… but otherwise only a blinking cursor and arrow on a black screen. I did the ctrl-alt-F1 and tried to get in… no avail.
I did try all the tricks I found here and on Ubuntu and the web to help figure out getting into the desktop. But after more then a week, I simply decided to sweep clean and reinstall (yes my data is backed-up on the cloud)

… but the nightmare was made worse.

I reinstalled on the SSD (sdc). I had error messages about partman. I did it over, again on sdc… so I went away for the few mins it takes to complete…error from my part, here.

Next thing I know is that the SSD cannot be booted, the main drive (sda for windows) is wiped out with an uncomplete install of UM ( I can see the drives using my UM flashdisk). AND the BIOS (UEFI) boot order is frozen with a password unknown to me (i.e. supervisor password that can’t be changed) - which I could access easily before then.

Did read somewhere (after the fact) that these Acer are not Linux friendly… they may be right.

Now I’m stuck over a long week-end here, with a computer usable only with using my UM flashdisk…

My patience will lead me to the store and being less heavy by a few bucks, I guess.