When you open a new 'Write' message: the From address should be auto completed. the cursor should be in the first TO field ready for you to type email address. If you click on the Contacts Sidebar to select eg:address book or anything else in another window etc, then the cursor will disappear as focus has been moved away.

Use the mouse to position and left click to select where to put cursor. Do you get a cursor?

When you say 'The message box is empty.' Please clarify your comment by posting an image of the Write window.

Test: Help > Restart with addons disabled then click on 'Write' and see if there is any difference.

If Write now works ok, then one of your addon extensions is causing a conflict. You would need to disable one at a time to work out which one is causing the problem.

Toad-Hall said

When you open a new 'Write' message: the From address should be auto completed. the cursor should be in the first TO field ready for you to type email address. If you click on the Contacts Sidebar to select eg:address book or anything else in another window etc, then the cursor will disappear as focus has been moved away. Use the mouse to position and left click to select where to put cursor. Do you get a cursor? When you say 'The message box is empty.' Please clarify your comment by posting an image of the Write window. Test: Help > Restart with addons disabled then click on 'Write' and see if there is any difference. If Write now works ok, then one of your addon extensions is causing a conflict. You would need to disable one at a time to work out which one is causing the problem.

I ran Malwarebytes & restarted the computer and now it works. It was strange, because I could add addresses to send to and a subject, but when I left clicked in the message box the cursor wouldn't appear and I couldn't write or paste. Thanks for your help.