Desperate: "Could not initialize Photoshop because an unexpected end-of-file was encountered."

Are you opening Photoshop by opening a document? "Unexpected end-of-file" usually refers to a corrupt document.

But if you get this by launching Photoshop from taskbar/start, you should uninstall and reinstall. That should fix any damaged program files.

I don't see how this has anything to do with preferences. That's in your user account, not the program files.

Generally, there's always a slight risk in uninstalling older versions with a newer version still installed. Some still needed components may go out with the uninstalls - most commonly the file associations, but I suppose other things could possibly happen too.

So in the future, always follow strict version order. The safe way to do this is to start with the newest version and work backwards. Last in, first out. Once you've uninstalled all of them this way, reinstall the one you want to keep.