did it used to work recently on this computer ?
if so you can try a system restore to a day when it was working
if that does not work i might be able to fix it for you but i would have to log into your computer remotely to see what happened. It either lost the mail boxes or the profile that says where they are or something else silly like logging into the computer with the wrong user account or clicking the wrong icon when you have 2 copies of eudora.
System restore instructions - windows 7 or 8 or 10
hold the windows logo key down and hit Rtype rstrui.exe in the run box that comes up and hit enter
select restore to an earlier date.
Under the "suggested restore" which is usually not old enough to help is a link for "OTHER RESTORE POINTS"click that if the suggested ones are not BEFORE THE PROBLEM STARTED
choose a date that is BEFORE you experienced the problem
hit ok / restore
the computer will start to shut down
a restoring settngs box will appear with a status bar
when it finishes your computer will restart with the same settings it had on the date you restored to. your data will not be affected.
It is not perfect. But it fixes a lot of things.