My tower is now a CLI machine. I thought it was an easy update from Xubuntu 16.04 to 18.04, but all I did was expose a problem with the hardware. I tested several other things, and while the sensitivity varied, every Linux distro experienced lock-ups on the GUI. So I installed Debian 9. The lock-ups were less frequent, so I was able to get everything installed and my files restored from backup. Then I switched away from the X session and I’m using the commandline interface.
This will be a good way to reacquaint myself with the CLI. As we say, I’ll be renewing my membership in the Brotherhood of the Commandline. The computer works perfectly fine otherwise, and I have no trouble at all logging in from the laptop via SSH or Filezilla (SFTP protocol). It makes a good file server so I can keep the laptop uncluttered. It’s like having my own cloud at home.
My testing indicates it’s something wrong with the motherboard. As long as it keeps running, I’m not worried about replacing it for now. I can get everything done on my laptop.