Please start *Windows'* safe mode with networking enabled - win8 http://windows.microsoft.com/en-us/windows-8/windows-startup-settings-safe-mode - win7 http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-7 - 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? Please post with results.

In safe-mode it seems to work. Rearly faster than before. Which solution we will get?

Given your results, we now have these questions: 1. What antivirus and firewall are you running on Windows? 2. With Windows started in safe mode and Thunderbird started *normally* (not in safe mode), is system slow, or fast?

1. only Windows Tools, Windows Firewall and security Essentials 2. in Windows safe mode it seems that it's faster. The context menues and menues are opening earlier.

i Will Need a 64-bit Version of Thunderbird!

Because it is faster in Windows safe mode, something loaded during windows boot is slowing down thunderbird - perhaps MSE (Essentials). I've had MSE affect my performance, although I do not understand how the involvement of menus, I've not seen that.

Please see MSE item in https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues to make the adjustment, and post your results.