Thunderbird has stopped downloading my emails from the virginmedia server, especially if I have already viewed them on my iphone or ipad. It has also started asking for my password then saying that it can't be sent, so I can't send emails either.

I have a lot of saved emails that I can't afford to lose, so I was advised to save a copy on a memory stick and uninstall Thunderbird. I have done this and also cleared all the hidden folders then reinstalled Thunderbird, but now I don't know how to get the files from the memory stick back onto my 'new' Thunderbird. Help!