Unable to open Thunderbird get message: login to server failed.

When Thunderbird is opened on my Dell laptop the message: Login in to server (mail server).com with user name (email account address).com failed. The message has two options Retry or Enter New Password. Retry gets nowhere, same message appears. Entering the correct password for the email account also gets a repeat of the message. Checked the password in Tools/Options/Privacy & Security/Passwords/Saved Passwords and the password used is correct. Thunderbird was uninstalled and Thunderbird file in the Program Files folder deleted. Computer restarted and Thunderbird reinstalled. Same situation with same failure message displayed. The password utilized works with my desktop, iPad and iPhone Thunderbird account without fail. In addition when installed Thunderbird was selected as the default email provider. However, each time Thunderbird is opened the message requiring "Set As Default" selection needs to be made before continuing. Any suggestions on how to resolve these two issues would be appreciated.