Start *Windows'* safe mode with networking enabled - win8 http://windows.microsoft.com/en-US/windows-8/windows-startup-settings-including-safe-mode - win7 http://windows.microsoft.com/en-US/windows7/Start-your-computer-in-safe-mode - XP http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx

Still In Windows safe mode, start thunderbird in safe mode - http://support.mozillamessaging.com/en-US/kb/safe-mode

Does problem go away?

SDye said

I updated to version 38.0 yesterday and since then whenever I open Thunderbird it refuses to open and at the top shows Not Responding. I am forced to close it via Task Manager. What happened & how do I fix it?

I tried it in safe mode and it does open and I can see my mail but when I try again to open it in regular mode it just is the same thing. I'm planning on uninstalling and reinstalling, after running mozbackup. If that does not work I'm going to a different email program, as this is my work email and I can't miss it for more than a day or two. It very frustrating. But thank you for your suggestion.

I uninstalled & reinstalled and had the same problem. I tried to rebuild my profile, however in the directions from Mozilla on how to do this, I was not able to find my profile at the location specified. I then went to safe mode and disabled all my extensions, addons and plugins and finally got it to work. Of course, now I don't have any extensions or addons, making it somewhat less useful. I believe the problem may be due to silverlight, java &/or napi plugins. Good luck to anyone else having this problem.

Which antivirus and software program(s) are you running?

SDye said

I updated to version 38.0 yesterday and since then whenever I open Thunderbird it refuses to open and at the top shows Not Responding. I am forced to close it via Task Manager. What happened & how do I fix it?

Thanks, I was able to solve the problem by backing up using MozBackup, uninstalling Thunderbird and reinstalling it. I don't know what the issue actually was that was causing the "Not Responding" but it is working now. Thanks for your help.

Did you also restore using mozbackup?

FWIW, sometimes reinstalling the program helps anitivirus software "recognize" thunderbird. So it would be helpful for us to know which one you are using.

SDye said

I updated to version 38.0 yesterday and since then whenever I open Thunderbird it refuses to open and at the top shows Not Responding. I am forced to close it via Task Manager. What happened & how do I fix it?

Once I reinstalled everything was there so I didn't need to restore from Mozbackup.

I am running Windows 7 Professional, and using Microsoft Security Essentials for my Virus and Spyware detections. I also run checks for malware usually once a quarter. I use Rainlender 2 for my calendar and was also running Chrome when I had problems with Thunderbird, but am thinking of switching back to Firefox. Thanks for your help.

> I tried it in safe mode and it does open and I can see my mail but when I try again to open it in regular mode it just is the same thing.

This clearly suggests that something you added to Thunderbird or the OS is causing at least some of your trouble. If problem occurs with OS in normal mode and Thunderbird in safe mode - http://support.mozillamessaging.com/en-US/kb/safe-mode - then you should suspect a program that is loaded by the OS, like antivirus. But if http://support.mozillamessaging.com/en-US/kb/safe-mode does help, then the problem is related to an addon, or hardware accerlation found at tools | options | advanced | general

It happened again today when I updated to 38.4.0. Got the window, then the "Not Responding". I closed via task manager. I reopened in safe mode and looked at my plugins. All have been previously set to Never Activate except Foxit Reader and Last Pass. When I looked at Extensions I saw the Lightning calendar. Since I use a different calendar program, I totally removed Lightning. I then closed TBird and reopened it. It is working find now. Perhaps that was my problem all along. At this point I don't need any help, just wanted to pass that along. Thanks for your support!