Please reset the Lightroom Preferences back to default.
Preferences C:\Users\[user name]\AppData\Roaming\Adobe\Lightroom\Preferences\Lightroom 6 Preferences.agprefs
To reset your preferences in Windows, restart Lightroom from the pinned application icon in the Start Menu (Windows 7) or the Start Screen (Windows 8 and later), and immediately press the shift + alt keys. In the resulting Reset Preferences dialog box, indicate you want to reset your preferences.
Let us know if that helps.
Thanks for the suggestion, but ...
Pressing shift+alt does not result in a preferences dialog box. It opens a Select Catalog window. Then whatever catalog I select, nothing more happens. No Splash Screen, no Lightroom in Task Manager.
I have tried uninstall & deleting all LR folders in Program FIles then reinstall with no effect.
I suspect that it must be some registry entry that Adobe leaves intact when it should delete on uninstall; but I have no Idea how to find/fix this kind of carelessness on the part of programmers.
You're better off renaming the preference file (.agprefs) in the location shown above to ".old" so you can recover it later if desired. You're right that alt+shift presents the "Select Catalog" dialog box.
For what it's worth, I am running the 10586 build of W10 with LR CC 2015.3 (the same as LR 6.3) and it's working fine.
Have you tried opening a new catalog instead of choosing an existing one? It sounds like LR is silently crashing.
Mike, I've tried several different catalogs and even creating a new catalog. No Go. Lightroom never even becomes a task in task manager.
Does anyone know how to clean the registry of all LR entries?
You can uninstall the Lightroom using the Adobe Cleaner tool refer: Use the Adobe Creative Cloud Cleaner Tool to solve installation problems
Also, you can delete Lightroom manually the system.
C:\Program Files\Common Files\Adobe*
C:\Program Files (x86)\Adobe*
C:\Program Files (x86)\Common Files\Adobe*