Well I am confused... really. I use windows 7 and Thundebird... no compatabvility issues at all.

So either your diagnostic is really a rubbish, or there is something truly unique about your Thunderbird version, like it is a pre release of version one or something.

OK I think I found the problem. Windows isn't the problem. Apparently yahoo changed protocols and now requires POP settings and I have been using IMAP. Of course they, yahoo charges a fee for setting up POP through Tbird Im tempted to download my contacts list and delete accounts with yahoo. Too many better providers out there to put up with this much longer.

Yahoo stopped or stopping IMAP....are you sure? There is nothing on their website, the help pages still refer to IMAP.

• https://help.yahoo.com/kb/mobile-mail/imap-server-settings-sln4075.html

Toad-Hall, I am guessing at this but here is what I found on Mozilla Help;

Yahoo! Service Offerings Yahoo!'s services vary by availability and rate based on the country where you are located. In order to use Thunderbird with your Yahoo! account, your account must use the POP protocol. As of April 2010:

   In Canada and the USA, Yahoo! POP Access is not free. In these two countries, POP access requires payment. The service is called Yahoo! Mail Plus.    In other countries, Yahoo! POP access is free. 

Yahoo! POP Settings Refer to Yahoo!'s instructions for Accessing Yahoo! Mail using Mozilla Thunderbird.

The odd thing is I set up TB using IMAP, used it 2 years and now it will not accept my password that is on file with TB. Somebody changed something but it wasn't me. I have updated TB, changed my password and it still doesn't work. I really do not want to switch to POP so if anyone has any ideas let me know.

We do not get much air time to edit those support documents and what your reading was accurate when I wrote it about 4 years ago. not Yahoo offers IMAP universally.

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.

Matt did both of your suggestions, disabled add-ons and restart, didn't work. Restarted in safe mode and in mozilla support found a link to run a diagnostic. First screen said it couldn't run in safe mode and next it said program was incompatible with windows 7. Being novice at this Im thinking best answer is a wipe clean and start over. Don't know what else to do. Thanks for the earlier advice, it was worth trying as a simple fix.

Restarted in safe mode and in mozilla support found a link to run a diagnostic.

My issue is this. Thunderbird has no diagnostics. Nor are there diagnostic links on the support site that actually execute programs or routines. Hence my difficulty.

I have no idea where you are or what this diagnostic is, other than rubbish, as Thunderbird is running here on windows 7 and has done through about 10 versions.

Perhaps you could get a screen shot of post it, perhaps that will help me understand.

Where is this "Mozilla Support" you found the diagnostic? some web site perhaps?

Starting over will not do any good. Whatever is wrong is not with Thunderbird, or very unlikely to be so we need to work out what the issue is.

Let me get this straight, you started Windows 7 in safe mode with networking. It popped up a warning that it was in a special diagnostic mode and you then executed Thunderbird and well, what happened exactly (Error message I assume, but what was it)?