I had to re-install Thunderbird on my PC.

Why? Even when re-installing Thunderbird this would normally not cause the address book to disappear. Is there something you haven't mentioned?

Also see http://kb.mozillazine.org/Moving_address_books_between_profiles

What does "re-install" mean? Did you also lose all your email accounts and their stored messages?

If you had just reinstalled the Thunderbird program itself, it would have not changed your profile and you should be as you were beforehand. So, have you done more than just reinstalling the Thunderbird program?

As far as I remember, I just re-installed T-bird. It came up with a clean slate; no addresses, no bookmarks, just as if it was being installed for the first time. I have been told that that info is stored somewhere, I just don't know where to look.