I went on-line and followed the instructions on copying and pasting the data to a new drive.

What instructions? Please post a link.

Copy the entire Thunderbird folder from the old computer to the new one:

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

I did as the video suggested....but on the new computer, my newly installed Thunderbird doesn't pick up the Thunderbird folder that I copied and pasted from my old computer to my external hard drive...so I'm still with a new Thunderbird on my new computer without any of the data from my old Thunderbird client....Mike

When you copy the Thunderbird folder onto the new computer, don't try to overwrite the existing Thunderbird folder. Delete the existing folder and then copy the other one into the same place.

Make sure the Thunderbird folder is a subfolder of C:\Users\username\AppData\Roaming not C:\Users\username\AppData\Local.

The path you suggest to copy and paste the Thunderbird folder is not on my new computer (Widows 10)....you ask that I copy the Thunderbird folder to C:\Users\username\AppData\Roaming however, on my C drive, I only have C:\Users and when I click on Users I get two folders mikeb (I suppose that's me as I'm mike broad) and public...there is no "username" folder, no "AppData" folder, no "Roaming" folder. So I copied Thunderbird onto C:\Users and I opened up the Thunderbird folder to look for an .exe file to open the program. I looked in every folder and there was no .exe program??? Please adivse...thanks. Mike Broad

The username is your Windows User Account name, in this case mikeb. The AppData folder is hidden by default; to show it see this post.

I did what you asked ...got the hidden files shown...put my Thunderbird in the Roaming file...then I went online and downloaded Thunderbird..and the new installation picked up the copied file..many thxs for hanging in there with me..Mike