And the error message is? We know exactly what you tell us. At this point I now "The program won't open due to an error message"

The error message is OXc0000005

make that: 0xc0000005 (if it makes a difference)

That is a windows system error. Most probably your hard disk is failing, you have a malware infection or your anti virus is not functioning correctly. More information here https://www.stellarinfo.com/blog/how-to-fix-error-code-0xc0000005-in-windows/

I suggest you try the chkdsk solution offered.

I also suggest you try Thunderbird safe mode as anti virus programs routinely act like a virus and inject stuff into Thunderbird. Holding the shift key while starting Thunderbird will enable safe mode. Continue what prompted (if you get that far without the crash)

Thanks, Matt. I'm afraid the chkdsk didn't work and I can't get the program to open in safe mode but I may try starting the computer in safe mode and see if it works in that mode. Time to hit the sack. Thanks again for the suggestions.

Have you tried doing a full reinstall from thunderbird.net

That worked! Thanks!