Summary:

Bleachbit has done something bad to my laptop (Lenovo running
Linux Mint)

Planning to travel with my laptop for first time in many years,
thought it would be a good idea (was paranoid about laptop being
'read' somehow..mostly finances, personal health, nothing too
crazy, and now wish I hadn't run bleachbit at all) Anyway 
starting with Menu, seraching "bleachbit" and clicking "Bleachbit (as
root)" and then followed simple directions on, I think it was
https://www.howtogeek.com/116971/7-tips-to-get-the-most-out-of-bleachbit-a-ccleaner-for-linux/
(File Shredding section and Wiping Free Disk Space section  of
directions. The latter said " If you only have a single drive, the
default settings will work fine." so I went to send step)

It was "After configuring the options on the Drives tab, enable the
Free disk space option under System. As you’d expect, this option is
very slow – so BleachBit warns you." then click ok

I ran it and it said it will need 60 minutes...I watched the first
couple of minutes then went away...checked periodically..last I
checked, 40 or so minutes left...

Later, returning to check progressi again, and it seemed to have gone
into screensaver mode (or so I assumed, rather than bigger problem..and
still that seems a possible interpretation) and it would respond to
the mouse but not more..did not give me ability to use password to get
out of screensaver back  to view laptop)

Now, I knew it would be a bad idea to reboot in the middle..luckily I
had kitchen timers from back when it said "40 minutes" before it's
done..to be on the safe side I waited a good 10 minutes beyond
that. Then (the thing still not being responsive to unlock
screen..just mouse cursor (moveable) being shown)..so then (10 minutes
or so after it should be done) is when I did a hard (long press of
power button) shutdown...Then rebooted.

Of course, given how messed up things are (see below) it seems more
likely that it was not a case of "you somehow shut down halfway
despite giving it 10 minutes extra" but something bigger went
wrong. Instead it was not a screensaver but already a problem
situation thanks to bleachbit, is what I probably saw.

-----

Now: "0 bytes" of space left, basically. I can launch firefox 
and run Terminal..but not much else. Try to take a screenshot? Nope. No
space. Etc. Error message, transcribed:

"the volume "Filesystem root" has only 0 bytes disk space remaining"
You can free up disk space by removing unused programs or files, or by
moving files to another disk or partition"

It offered to let me "Examine" and when I said yes it took me to "Disk
Usage Analyzer" which shows "/" as 100% (full) with 22items and 42.0GB
though "home" inside it it at 86.5%  and  36.4GB (I'm under
/home/owner inside which is Desktop, Downloads etc) User   10.9%
So these must mean not what percent full but what percent of
total (86.5%+10.9% and /var/ at 1.5% and smaller for the rest adding
up to 100%) aka what "Usage" means.

Cannot even save screenshot on USB (trying to be resourceful..)error
was something l ike, no space to mount usb...ugh.

ABOVE IS THE MAIN SUMMARY. MISC ADDENDA:

Cannot log into gmail...enter email address...click "next".. just syas
"transferring data from accounts.youtube.com..." and stays that
way....I am guessing it's because there's "0 bytes" left so it cannot
save cookies or similar data on my disks...

Update: After another 2 reboots, OpenOffice isn't  working now:
"Either another instance of LibreOffice is accessing your personal
settings or your personal settings are locked. Simultaneous access can
lead to inconsistencies in your personal setttings. Before continuing,
you should make sure user " closes LibreOffice on host " "[I typed
that correct; it usees a single double-quote " for both of these]
Dialog ends "Do you really want to continue?" Click yes, get:
"LibreOffice 5.0 Fatal Error" and "The application cannot be
started. Failed to
updatefile:///home/owner/.config/libreoffice/4/user/extensions/bundled/lastsynchronized"
(The only thing I recall doing besides rebooting twice more was to set
the laptop's password back to what it was when I got it from Best Buy
in prep to having it be service by you)