Have you entered your new password in Thunderbird?

Someone correct me if I'm wrong, but I think Thunderbird won't ask you for a new password if the one it keeps isn't valid anymore. Note that Thunderbird doesn't know whether the reason it cannot log into the server is that the password has changed to begin with. The reason could be (and in fact it usually is) something else.

You may make Thunderbird ask for the password the next time it connects to the server by removing the old password from Thunderbird, or you may use the same procedure to simply update the password instead:

1. Go to Settings > Privacy & Security > Saved Passwords.
2. Click Show Passwords if you want to change the password instead of removing it. You won't be able to edit the password unless you do this first.
3. Look for the password that has changed.
4. Either select the password and click Remove to make Thunderbird ask for it the next time (make sure you've selected the right password before removing it), or right-click on it, choose Edit Password and type the new password there.
5. Restart Thunderbird if the problem persists. You may need to do that for the changes to take effect, not sure.