JeffSL said

The lightning icon has disappeared, so there is no way to access my calendar. Reboot does not help. I tried to reinstall lightning and nothing happened. What do I need to do to get my lightning calendar up and running again?

The problem has been resolved. Never mind. Thanks

How did you resolve it?

I reinstalled Lightning. It did not work the first few times I tried it. So, I persisted. Eventually the reinstall worked and all the old entries were still there. I am not sure how many times I had to try it. Maybe six times or so.