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.

Many Thanks Matt, that pointed me in the right direction. It worked fine in safe mode with networking so I tried uninstalling recent software including Windows updates. Getting nowhere I suddenly remembered Id recently upgraded Avast Anti-Virus about the time T/bird stopped working. I turned of the Avast shields and, TA DA - Working! Narrowed it down to Avast mail shield, but is not a great situation to have one of your shields disabled even just because you are bugged icon-wise. So i tracked down this fix; http://www.warriorforum.com/main-internet-marketing-discussion-forum/187513-avast-blocking-your-email-heres-fix.html Now its not for the latest version but if you follow the instructions and find the corresponding locations in your version it should work? It did for me and I have no aggro with the Avast icon!

Regards. Paul