Your ISP gave you a password for Thunderbird??
Is it a password to open the Thunderbird program, or is it the password to access your pop email account?

I've used Tbird for years, and no ISP ever gave me a password...I chose my own, for the master program access and my pop email accounts..

When you get Tbird all set up and your favorite browser too, you can copy & save/back up your profiles for each and save them to a usb flash drive or such.

It is so easy to have the back up profiles in case of a crash & reinstall, or new machine..
how to - profiles
https://support.mozilla.org/en-US/kb/profiles-tb

If you can access files on the old hard drive you might be able rescue the profiles on it. Did the old hard drive fail or something else on the old laptop?