When I launch Thunderbird after downloading an update I get a message that says 'the installation seems to be incomplete. Check your hardware (what hardware?) and disk set up and/or reinstall. How do I check hardware and disk? If i reinstall will I lose my old messages?

I wish thunderbird/firefox would stop behaving as if everyone knows how to repair these things. I still haven't managed to stop thunderbird from asking for and often rejecting my email password, despite two kind people trying to sort it out.