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I cannot open Thunderbird. The process isn't running, but when I click on the icon, I get the the following error:

Thunderbird is already running, but is not responding. To open a new window, you must first close the existing Thunderbird process, or restart your system.

I've tried the following:

  • Ending the task in Task Manager
  • Deleting parent.lock
  • Uninstalling Thunderbird
  • Uninstalling Firefox
  • Running Thunderbird in software "safe mode" and Windows safe mode

What can I do to fix this problem?

The problem looks more serious than expected. I do not see any Mail folder in my profile at C:\Users\your-username\AppData\Mozilla\Thunderbird. I think I lost my email.

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I added your extra comment detail to the question. The path provided doesn't look right, Thunderbird is not in Mozilla normally. Where is the parent.lock file you deleted? And how were you able to end the task in task manager if the process wasn't running? – Paul Sep 23 '12 at 9:50

You said you've tried ending the task in task manager, but have you tried ending the process in the task manager?

Does it ever work correctly, for example the first time after rebooting your computer?

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While the steps you described seem inconsistent, the most likely cause is probably an inaccessible or missing profile. See the following documents for hints on this

I will update my answer with more details, when it becomes more clear, what you did exactly and which results you got.

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What I experienced yesterday must be a major bug in Thunderbird. I've lost all of my mail. The folder for my corresponding profile is completely gone in C:\Users\username\AppData\Roaming\Thunderbird.

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Uninstall and delete everything to do with thunderbird, then reinstall, worked for me, lost mail, but it's all on gmail anyway.

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Download Revo Uninstaller and then uninstall Thunderbird with that. Then reinstall Thunderbird. Also use Win+E to start Explorer, then browse to C:\Users\your-username\AppData\Mozilla and delete the Thunderbird directory in there.

Oh, by the way, Windows has notoriously bad process management, so be careful not to mess with the operating system.

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Will deleting my profile erase my email and configuration settings? What do I need to do to back that up first? – Robert Sep 23 '12 at 5:04
The problem looks more serious than expected. I do not see any Mail folder in my profile. I think I lost my email. – Robert Sep 23 '12 at 5:15
@Robert Yes, this would delete all your mail and settings so I cannot recommend these steps. Jonathan Reno should have put in a warning at least. The use of Revo Uninstaller is questionable also. – Gurken Papst Sep 23 '12 at 10:54

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