Sometimes Thunderbird doesn't recognize profile on an update. You can check this by clicking help>moretroubleshootinginformation, scroll down to 'profiles', click 'about:profiles' - and you should see a list of profiles. If there are two, one may be yours with the account info.

Hi David, Thanks for your reply, I checked the profiles and there were 2 so I changed to the other one but it made no difference. Would iI be better off deleting Thunderbird and reinstalling it? Regards Stan

Reinstalling Thunderbird won't fix this. The fact that there are two profiles still indicates that some remnants are there. To verify, try looking from Windows FIle Explorer. The profiles are at c:\users\<yourid>\appdata\roaming\thunderbird\profiles. in each, look in Mail folder for info on a POP account or in imapmail folder for info on any IMAP account. My hope is that one of the profiles will have that info.