To diagnose problems with Thunderbird, try one of the following:

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Hi Matt,

That was great..!!! :)

I restarted with Add-ons disabled (Thunderbird Safe Mode). Now folder has been recovered & everything goes fine now.

Now I've switched back to normal mode & enabled the same theme which i was using before now, but still works good. Will other disabled one's too can be the cause these problems..???

Regards, Siva.

Sometimes all that is required is a safe mode startup. I have no idea what actually resets in that process other than add-ons and graphics hardware acceleration. But sometime it fixes things with no further action required.

Thanks Matt..!! :)

You're doing Great Job. Keep Going..!! Rock It.!

Thanks, Siva.