FossaPup 9.0.5.
The problem is with an Internal SSD, in which the system resided. It all started from a CPU surge - which made me have to perform a Hard Shutdown. Then at boot - there was a Superblock missing, or something like that; and it didn't boot. I could see the drive from LiveUSB, and replaced something on the SSD with that in the USB*― so I could boot from the SSD; and continued to work from the system on it (which of course was a big mistake). After a couple of days - something wasn't responsive, and I couldn't shut the system*― so did a Hard Shutdown again. Since then - I don't see the drive in LiveUSB.
However there is a reason to think that it isn't totally broken*― because when I'm starting the LiveUSB with the Save File in an External HDD*― it doesn't work without the SSD in the computer; right at the end of the boot - the desktop doesn't come up; and does work with the SSD inside. A Computer Technician suggested that that's because there are some boot files in the SSD.
So is there some software that can do a deeper probing, to see whether the SSD works; at least to salvage the files from it?
If there isn't, or If this won't work*― I know I can give it to a Lab; so I'll research it then.

I think that you have lost your superblock on the internal SSD. There are alternative superblocks at intervals across the SSD. You can restore the superblock with the command fsck run as root and telling fsck to use the alternate superblock located at block x.

You can find out where the alternate superblocks are by running the newfs -N command as root. The -N tells newfs to create a new file system without actually writing anything on the drive. Along the way newfs will report where the alternative superblocks are among other things.

You can get the details on how to write each command here:
https://docs.oracle.com/cd/E19455-01...f0i/index.html

or here:
man fsck
man newfs

@jailbait - The drive isn't seen at all, including in BIOS; as if it doesn't exist.

Have you checked cabling? Firmly attached? Tried replacing them?

A Lab to recover the files... is that a way to say backups do not exist?

Does the SSD show up in the BIOS, maybe try plugging it into a different port on the board?

The drive was checked in other places\computers. I even gave it to a Computer Technician. So it's definitely the drive.
There's no backup. Interestingly, it happened right when I ordered a drive for backup, after 24 years of using a computer. I guess - fate.

Ouch. Lesson learned the hard way. I have backups local and off-site of data. Multiple backups in fact. Never know when something is going to go 'poof', dropped, broke, stolen, or etc. ....

Lesson learned before that... as I said - I was about to backup everything. The most important things remained; but still will be a great loss. Unless a Lab will save it.

MrAccident,

In the UK we have Essential Data Recovery who are excellent:
https://www.essentialdatarecovery.co.uk/index.html

There are plenty of charlatans offering data recovery, so please do careful research before releasing your SSD.

@beachboy2 - thanks. I was going to search by recommended\rating (and price).