Hahah, thank you Dutch_Master, Ram and of course Nelz who's had some fine patience with this rather newbie!!
Now, things have gotten a little better, hopefully I can confirm it later with more testing:
Ok. The last time I was forced to login in emergency mode it showed that I had 4 (or more) fstab swap files and was asked to choose one... I chose the one with the latest change date, (thinking it was the one I edited correctly) with the others eliminated automatically. I then shutdown
So after a reboot I was asked to login normally again, as the main user . That's when I got the warning message mentioned above. So, I tried from root and fortunately was able to enter my desktop with complete UI functionallity ok.
Since from the beginning problems arose from fstab, I decided to look it up ....to my surprise and due to my ignorance, during the last edit I had accidentally typed "shutdown" on the fstab file, thinking I had already exited the file; so, the only text in the fstab was "shutdown"!, nothing else!
So, I then looked up for a backup fstab file I had made way earlier, before I even came to the forums. Fortunately I was able to find it. Both the "new" modified, aka screwed-up fstab, and the old one were opened with kwrite. I then selected+copied all the contents of the backup and pasted over the contents of the "new" fstab. I then deleted, as suggested by Nelz the problematic line containing windows/ D...
I rebooted and now enter as main user password and can finally enter my work desktop normally!!!
I am not sure if everything is ok, so I will do some testing and then see what the external USB HD is behaving like.. and start over again if I need fixing (most likely) the external drive issues, but with Nelzs' early suggestions...
THANK YOU VERY MUCH!!!
I appreciate any suggestions you may have.
Will stay tuned! Thanks again everybody!! Hopefully I'll be able to leave you off the hook on this!!