I am NOT a developer, or even close, but I opened an account here just to thank you all for your time and the effort you put in to providing the solution. When a mere, practical lay-user such as me encounters a problem like this (the blank, black screen; hours-long time burden, and - worst of all - the apprehension that all is lost) it can be emotionally mortifying. I went with Matthew_schuiling's advice, and was gratified to experience that same, enormous sense of relief. Thanks to you all.