Thunderbird creates two profile folders, one in the default location

C:\Users\<your user name>\AppData\Local\Thunderbird\Profiles\<your profile name>

and the other in

C:\Users\<your user name>\AppData\Roaming\Thunderbird\Profiles\<your profile name>

I don't know what the purpose of the Local one is, but I have never backed it up or used it for anything. All the important data is in the Roaming profile. I have copied that many times to new setups and has always worked for me. I have never used the built-in Import feature (I've been told it can't deal with profiles larger than 2 GB) Here's my method:

- Assuming that Thunderbird is already installed on the new computer... On the old computer or on the backup disk, with Thunderbird closed, copy the entire profile I mentioned above to the equivalent Profiles directory on the new computer. Make a note of your profile folder's name.

- With Thunderbird closed on the new computer, press <WindowsKey>+R to bring up the Run box. In the slot, type "thunderbird -profilemanager" (no quotes). This brings up the Profile Manager where you can Create, Rename, and Delete profiles.

- Choose Create..., then where it says "begin creating your profile, click Next...

- The new profile name can be anything you want. Click Choose Folder and select your backup folder that you just placed there. When you choose OK, you will find yourself back at the Profile Manager. You can choose your newly created profile and also choose to go immediately there when you next start Thunderbird. Choose "Start Thunderbird" and things should be pretty much back to normal.

Thanks for the advice Lin. I've just tried the method you suggest, and I'm afraid it's still not working. That's why I'm worried that the backup folder I've been saving is incomplete or the wrong contents. It contains folders called '$Archive', 'Cache2', 'Safebrowsing' and 'StartupCache'. Does that sound right? If not, I fear the only hope is to attempt data recovery from the dead disc drive.

The profile you recovered from backup seems to be the one in "local". I am not sure what that is, but it is likely scratch space for temporary use. Your TB profile should have folders like Mail, ImapMail, chrome, etc. Your emails are in those Mail and Imapmail folders. The import feature only works on files that were exported.

I am not familiar with your backup program. Perhaps you have the profile somewhere else within your backup? It looks like it depends on which folder you decide to back up. Look for the TB profile from your backup in the tree of C:\Users\<your user name>\AppData\Roaming\Thunderbird\Profiles\<your profile name>.

Like Mark says, you seem to be trying to use the Local profile. The important one that a sub-folder in Roaming will have many sub-folders. If you don't have a good copy of that, you're probably out of luck. Here's what mine has (there are certainly some old, obsolete folders from versions and add-ons gone by):

<DIR> blocklists <DIR> browser-extension-data <DIR> calendar-data <DIR> cardbook <DIR> chrome <DIR> crashes <DIR> datareporting <DIR> extensions <DIR> extension-store <DIR> extension-store-menus <DIR> extension-store-userscripts <DIR> gcontactsync <DIR> gmp <DIR> ImapMail <DIR> lwtheme <DIR> Mail <DIR> minidumps <DIR> News <DIR> Photos <DIR> saved-telemetry-pings <DIR> scheduled-notifications <DIR> security_state <DIR> settings <DIR> shader-cache <DIR> storage <DIR> TbSync <DIR> TestPilotExperimentFiles <DIR> US <DIR> webapps

Thank you Mark and Lin. Unfortunately the profile I've been trying to use is the only one for which I have a backup, so it seems that I had set up the backup program wrongly. Useful lesson for the future! So now my only hope of retrieving the correct profile folder is if I can get it recovered from the drive that died. I've got a data recovery specialist working on that now, and I'm waiting for the outcome...

If you have been using IMAP for your emails, you may have them all still on the server. If you create a new TB account to that folder, IMAP should sync all your old files into the new TB folder. It might take a while.