The Message Pane is toggled on and off by pressing F8.

But from your description is sounds like you are viewing the top level account screen and do not have the Directory Pane showing all accounts and folders down the left margin.

From the Menu Bar select View-Layout-Directory Pane

The Message Pane is also available under the View-Layout menu.

Yes, I have the directory pane and all the accounts and folders down the left, but wherever I click there the right hand side still shows the same.

I am seeing two panes. The one on the left which shows the accounts and folders and the one on the right which never changes and which is the generic thunderbird top level window as if you had clicked on the root folder on the left.

There is no message directory listing pane or message viewing pane, have tried F8.

Any other suggestions?

There have been reports of display problems with the new version. The suggested fix is to turn Hardware Acceleration off.

It is under Tools-Options-General

I have not upgraded to version 38 due to the issues. I never do upgrades until the dust settles on any major version change.

This is a hardware issue? It works fine when I open a second pane.

I do not know. Just throwing out a suggestion based on questions and solutions I have seen . Do not follow it if you do not want to. I have no more to offer you. Like I said, I do not run the buggy version 38. Maybe someone else will have something for you.

Have you got the extension Thunderbird Conversations installed? If so, you are probalby left with version 2.8.1, which does not work with Thunderbird 38+. Go to https://addons.mozilla.org/de/thunderbird/addon/gmail-conversation-view/ and download the latest version (2.10). This worked fine for me.