Does your shortcut link to: "C:\Program Files (x86)\Mozilla Thunderbird\thunderbird.exe"

Check if the dirctory is "C:\Program Files (x86)\Mozilla Thunderbird" and it contains Thunderbird.exe

Try starting TB from Start / run : thunderbird.exe If that started but didn't work try  : thunderbird.exe -safe-mode

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode).

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.

The problem was solved by uninstalling Avast Antivirus software. Apparently there is a problem with the latest version of it that had applied yesterday. Also It is weird that disabling Avast didn't help.

Thunderbird will not open for me either. I have Windows 7 (x64) It worked before today. I don't have Avast antivirus. I have Norton

If you want an answer you need to open a new question.

This q was closed (a solution was found) and the only one reading this are those who answered to this one and haven't stopped email update.

(Norton is also problematic, try whats suggested)