and do you see any sort of error message? It is fine you have gone thorough "your troubleshooting suggestions" however those in this forum know exactly what your tell us. Personally I don't know what that means. Have you tried your system in safe mode with networking? That is a most fundamental troubleshooting suggestion. What about Thunderbird in safe mode? (troubleshooting mode from the help menu and continuing when prompted.)

message says login to server per my email failed