Make sure the Work Offline option under File > Offline is NOT checked.

Sorry, thanks for the suggestion, but this does not help. The "work offline" option was in fact unchecked already.

Could you elaborate a bit more on "the Thunderbird page does not work at all"? Do you get a specific error message? Is so, what is it?

To diagnose problems with Thunderbird, you can 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.

Thanks for your suggestions. On the advice of a friend, I right clicked on local folder, clicked on inbox, and the problem was fixed.

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem (even if it's yours). This will help other users with similar problems find the solution more easily, as it places it at the top of the discussion.

Thank you for contacting Mozilla Support!