I am unable to add a new case.
More information would be helpful - OS, version, etc. Did you see any error messages? What do your top menus look like? Do they start with “Case”? If so, can you create a case from there? If not, I’d suggest deleting your user folder as described here:
I fixed this issue. I had to delete and reinstall. The splash screen never showed up with the options to add, open or close case.