have you rebooted your PC? If so, 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,

Thank you for your response. I had tried the first option already, I'd disabled the add-ons and it still didn't work. I used your reply to try and open in safe mode but I didn't write it down and so I didn't get the full way down the pathway in the links you posted and so I exited to login in again to read the path. When I logged in the emails downloaded. That seemed to resolve the issue.

Previously the green bar in the bottom right corner took several minutes to disappear from the screen. I don't know why. Is this a factor ?

Now that it works does this mean I have a virus ? I do use AV software that I've bought rather than one of the free ones. Do I need to do anything or will it be OK now ?

I really appreciate your help, I am very grateful.

Regards, Matthew

I doubt you have a virus... these things are often related to the anti virus product. A re boot or a start in windows safe mode jogs them into functioning correctly.

Always. The first step is restart the device. Be it a phone, a television or a computer.

Thanks