If nothing is coming in or going out, perhaps you have recently updated Thunderbird. check your Firewall/Anti-Virus program. Sometimes, Firewall/ Anti-Virus programs can seem to not realise that there is a new version of Thunderird and they block the TB Program. Close Thunderbird. Access your Firewall/Anti-virus program and make sure Thunderbird is allowed. Once I had to set as block and then reset to Allow to get it to work. then restart Thunderbird.