I am still a newbie when it comes to Linux in general. I work with Centos and Redhat at work, but at home I have installed Kubuntu LTS versions over the past 7 years or so on a couple machines. I just upgraded my wife's machine to Kubuntu 18.04 LTS and used the default KDE Plasma. Installed a bunch of programs and everything was working perfectly for months.
Then I started to rebuild my machine from 12.02 I think, to 18.04LTS. Lately I have not had much time to devote to rebuilding the machine, so it sat for weeks before I got back to it. Just as I was starting to work on my machine again, my wife asked what could be the issue with hers. Turning on the machine it boots to the login prompt (quiet) and no splash. This was set since the beginning. After logging her in, the background loads with the Home and recycle bin, then goes black. The hard drive goes dormant with a few flashes once-in-a-while. CTRL+L will Lock the screen. CTRL+ALT+DEL will show the log-out/reboot screen. I cannot get a terminal window (CTRL+T) or any other shortcut keys (that I know of) to work.
I searched the black screen issue only to find solutions from 2015 era that I cannot utilize since shortcut keys do not function.
The only thing on the screen is a mouse cursor.
Where do I go from here?
What do I need to find to diagnose this and how do I get it to run when most everything is gone?

I really hope someone can help. I do not feel like rebuilding this machine again.