Are you just transferring mail folders, or do you want to transfer accounts and settings as well?

Just folders.... it seems the account and its settings transfered but the folders did not. copied and pasted to and from a thumb-drive.

First, it may be easier to repeat the copy process of everything. If that option is open here are the 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

If that option isn't available, You can still do it another way.

- click help>troubleshootinginformation - scroll down to 'profile folder' and click 'open folder' - exit thunderbird - the folders for a POP account are to be copied to the Mail\<POPaccount> folder and local folders are to be copied to the Mail\Local Folders folder - now, locate those folder on the old computer, which will be in approximately the same location. They will likely appear in sets, such as inbox, inbox.msf, sent, sent.msf. You can ignore the msf files as they will be reconstructed by thunderbird

If you need more assistance, please post screenshots of your profile folder in each computer.