Hello,
Sorry to hear you are having trouble with your ThunderBird setup. Without seeing your settings, I cannot give any specific advice. Note that in Step 6 of our Thunderbird setup article, the username is the entire email address. By default, it just supplies everythign before the @. Be sure that is set correctly as it is the number one issue people run across. If you are a customer and still have issues with the Thunderbird setup, you will want to speak with Live Support so they can go over your settings individually.
Kindest Regards,
Scott M