When opened, Thunderbird displays new messages in inbox. They cannot be accessed or deleted. Mouse pointer will not activate any function by clicking left or right mouse button. "Inbox" is highlighted in blue, as well as messages. Eventually those words turn black, but still cannot open for awhile. Later (time varies), Thunderbird works properly. Windows (7) task manager shows very little cpu activite and memory usage is minimal. Task Manager can kill Thunderbird process, usually.