Can't open a project from an already open project.

I using Unity 5.6.3f1. I have an open project. I decide I want to work on another project. If I select "File" then "Open Project", Unity closes as expected but does not re-open. I know it takes a w$$anonymous$$le, but it should not be in minutes. If I re-start Unity and open the project from the splash screen, it opens fine. I never been able to get t$$anonymous$$s to work from an already open project.