Try trashing your InDesign preferences:
Close and relaunch InDesign, and IMMEDIATELY hold down Ctrl + Alt + Shift (Windows) or Cmd + Ctrl + Opt + Shift (Mac), and respond in the affirmative to the dialog asking if you really want to replace the preferences. you must be extremely fast on the keyboard (if you don’t see the confirmation prompt, you were too slow).
You may have to do it a couple of times before you get the hang of it!
Thank you Derek. I was successful on the first try, and was very hopeful. But the program is still doing the same thing. I have a couple of weird hints that someone might be able to help with:
If I click on a tool, it seems to select that tool only after I click again, on a different tool.
If I click on something that opens a dialog box, the SHAPE only of the box appears in front of anything I do on the computer (like this browser window) and the program freezes, until I shut down indesign again by turning my computer off.
I can perform simple commands like selecting an object and deleting it. I can move between pages but it's very jumpy and slow.
More experimenting: When the SHAPE of the dialog box appears, I can move it by click-dragging the bottom of the box, as if it were active. I clicked around the area where the "cancel" button would be and it closed. It's as if the dialog box comes up with no visible graphics showing what to select, just the shadow is there.
I am working in the links panel, trying to change the link of one of my objects to a different PDF.
I have found a temporary work around, so I can at least complete my newsletter today. I downloaded a previous version of Indesign (CC 2015) with instructions from this page: How to Find and Install Previous Version of Adobe Apps in CC 2015 | Adobe Customer Care Team
This version seems to be working fine. So I'm guessing there's a compatibility issue with CC 2017 and MAC OS Sierra 10.12.1 that may be resolved if others are having this problem too. I will look for that to be resolved with an update, hopefully.
Hope this might help someone with a similar emergency.