"The folder Inbox is full, and can't hold any more messages. To make room for more messages, delete any old or unwanted mail and compact the folder." 

When i sign into Thunderbird on my computer with windows a pops up saying "The folder Inbox is full, and can't hold any more messages. To make room for more messages, delete any old or unwanted mail and compact the folder." while locking the page from all any any activity. Then I can't click in anything else, nothing not even mail box & I can no longer even close Thunderbird without a complete computer forced program shut down. I could not compact emails previously and the unread emails are over 1056 and others are much larger. I was taking them out into a storage area but got busy and ignored the messages full warning. I had undated to a newer version of Thunderbird and removed some messages but got busy and over ran some type of block the FROZE the program and upgrading does not work again. How can I UN-freeze so I can really empty important email messages?