It seems like a Graphics driver problem. You may need to go to the card maker and update the drivers...
Note: not Windows update, but the card maker.
Thank you for the quick reply and your suggestion. I read the troubleshooting page.
It seems the problem is actually pretty simple: my laptop is too old! I purchased it in 2011, and as I recall, it came with Windows XP on it, or maybe Windows 7. In any case, I was pleased that I could update Windows to W10.
I downloaded the most current driver listed on the Dell website (dated 2013), but it wouldn't install. Dell doesn't support Wiindows 10 on this machine, so I suspect that's why the driver won't install. I think I'm at a dead-end, and it may indeed be time for a new laptop. Having said that, PSCC 19.0 and LR Classic CC are running fine (so far), except as noted above. I will not be surprised to encounter more issues as I use PS and LR.
Again, thanks for your help.
You're welcome. This should give you an idea of what cards are tested for Photoshop CC 2018 and it seems cards older than 2014 are hit and miss. Photoshop graphics processor (GPU) card FAQ
You can install and run earlier versions that will work until you are able to upgrade the hardware. I would recommend CC 2017.
The graphics processor in my 2011 Latitude is definitely not supported according to the GPU page you linked to. I'm actually surprised PS and LR are working as well as they are.
I will go back to 2017 as you suggested if I discover more problems. I can live with the white boxes!