I suggest you try a reboot. Switch off the power to your PC and then boot up again. Windows,10 'fast start' seems to cause an issue after an update. If that doesn't fix it, try resetting your Lightroom preferences and then rebooting.
I've rebooted several times (first thing I tried) . . . I then used system restore to reset windows to a date when lightroom was working (2nd thing I tried) . . . neither of those worked
I'm not sure which preferences that you want me to reset, but I went in and "reset warning dialogs" (that was the only thing that it looked like which *could* be reset) and restarted lightroom, and that seems to have fixed the problem.
- Press and hold the Shift+Option keys when double-clicking on the Lightroom application icon to launch it.
- Lightroom will show you a dialog asking whether you want to “Start Normally” or “Reset Preferences”. Click “Reset Preferences” to start Lightroom with a clean user preferences.
Nb. You will lose presets such as custom crops in print module etc.
When resetting preferences it doesn't delete any Presets you have. Those are separate files in a completely different folder from the Preference file.