Can you show a (partly anonymised) screen shot of your "Inbox screen" without the "instructions page", whatever you mean with this expression?

we now have three of these. I am closing then as I find them, but the original poster appear to be replying by posting a new topic.

Further to my earlier I think I have managed to get a screenshot of my Thunderbird inbox page, below. I am not sure it will be of much help.

Before the problem started, there was normally an instructions box visible on the screen when in Thunderbird. This box included instructions such as open, close, delete etc files. Now that box (at least I recall it as a box) does not appear. Now, eg, to delete a file I must right click on the file and hit the "waste" bin. I would have added a screenshot of one of my in boxes but I cannot get the screenshot key (Prt Sc) to work. What it would show, if I was able to print it, is an inbox screen without any instructions box.

which I have now locked. Please continue the discussion in this topic going forward.

I don't know what exactly you are looking for. But compared with the standard (default) view of a Thunderbird main window yours is missing the Folder Pane in your screen shot.