It's likely that some other program is interfering hence why Thunderbird is not responding. The most common culprit is an Anti-Virus which maybe doing any of the following : scanning various files in the profile when they open or scanning any emails which may be attempting to get downloaded etc. Do this: Access Anti-Virus product and make the Thunderbird profile folder exempt from scanning. Also temporarilly stop Anti-Virus from scanning any emails or files that get downloaded. Then start Thunderbird to see the effects. The proper method of testing whether you have a program or Anti-Virus etc causing the issue is to do the following: * Exit all programs. * Restart Computer in 'Safe Mode with Networking' mode. If you use a wireless connection then you may need to use an ethernet cable to connect computer to router whilst testing. * Then start up Thunderbird.