Fixed it!

Found the following from a 2005 forum post

Let's try to Return to Factory Settings from outside the program.

*With BiaB completely closed down, navigate to your bb folder and locate the file named, "intrface.bbw" and move it out of the folder. Okay to drop it onto the desktop or into any conventient folder you want other than the folder where BiaB lives.

Now start up Band in a Box, it will rebuild that file and perhaps correct whatever got corrupted to give you the black screen.

@ http://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=268506&site_id=1

That did the trick. Don't know how I got there - BIAB 2015 had been working fine in same configuration.