Do you know what you changed?

There are several things that might hide messages.

First check you have View|Folders|All

Make sure the QuickFilter Bar buttons are all un-selected.

If you have the Mail Views tool on the toolbar, make sure it is set to All.

Try dragging your mouse over an apparently empty listing. Sometimes (I don't know how) people get invisible white text on a white background, so the messages are there but invisible. Selecting them inverts and highlights them.

I found out what changed using your suggestions. Under View..Threads, ALL was not selected, clicking on that the Inbox messages were visible.

Which brings me back to what I was originally trying to accomplish, how do set Threads so that messages received are visible immediately if they on a thread. Currently if a message is received on a thread, I have to hunt to find it. Thanks for the help.

I use View|Folders|Unread to quickly find folders containing new messages. And the Unread switch in the QuickFilter Bar.

Not to mention an "Unread" Saved Search folder.

Yours seems to be a common reason for folk not liking threads. I very much like having related messages filed together and collected in a conversational thread. So I use that Unread button on the QuickFilter Bar a lot.

For many users the preferred course of action seems to be to disable Threading. View|Sort By|Unthreaded, but that's too drastic for me.

Thanks for the suggestions. Using a new computer and Thunderbird installation, old computer/thunderbird not the same.