I open message in inbox, read it, close it, message is gone. HELP?

I open Thunderbird and find three unread messages. I open and read one message. I close that message I do not delete it. After I close the message it is no longer in the in box. I go manually through folders. Still cannot find it. I do a search and it will be found in my inbox. If I open it while in search I can read it. If I go to Inbox it is not there but search says it is.I go back to Search and open the message again. This time I move it to Inbox. I go to Inbox and it is not there. So I go back and Copy it to Inbox, still not there. If I move or copy it to any other folder it will show up in the folder I send it to. Except for Inbox, still no show. I hope I described this well enough. It is very difficult. I get confused just trying to keep it simple. I have never had this problem. I have had about 3 Thunderbird updates since it started and the still have the problem. I have stopped Sync. That did not help. I have Windows 7. I have always used Thunderbird as my default email. I sure hope someone might have a solution. Thank you.