Please be more specific in what you did. I presume you have thunderbird and profile on old computer, and you're setting up a new computer? If that is the situation, here are my suggested steps:

Here is the link for moving a profile in Windows when installed in default location:

https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer

here is the info in brief steps:

1. ensure thunderbird is NOT running on old machine
2. enter %appdata% in search window on task bar and press Enter key
3. this should open windows file explorer in Appdata\roaming folder
4. highlight the Thunderbird folder and copy to external media
5. ensure thunderbird is installed on second computer and NOT running
6. enter %appdata% in search window on task bar and press Enter key
7. you should be in Appdata\roaming folder , copy&paste the exported Thunderbird folder there. This may prompt to overwrite an existing folder of same name. allow it
8. start thunderbird and all should be there

Thank you, David, for providing such a simple solution, which worked. I had spent fruitless hours messing about with Profiles, zip files etc, to no avail. Now ready to carry on working!

I was glad to assist. :)