A long time user of (2) computers, both running (2) separate accounts until now, but after having to re-install a fresh copy to one computer, I am no longer recognised on it while the other computer still continues functioning quite admirably ?

Firstly, both laptops are working well. While one is still behaving quite normal, I am unable to install Mozilla Thunderbird on the other after having done a reset .. The "HUB" will NOT except my personal details i.e. email address & PW which I've used for years. I'll leave it at that for now ..