Make sure your graphics driver is up to date. Make sure the 'Firewall' has 'thunderbird.exe' program as an allowed program. Suggest you also stop your Anti-Virus from scanning Thunderbird profile folder. You can check to see if the Anti-Virus is interfering by doing this. * Exit Thunderbird * Restart the computer using 'Safe mode with Networking' - if you normally use wireless conection you will need to use an ethernet cable to connect computer to router whilst testing. * Start Thunderbird.