First, let me apologize for not posting right away -- frankly, I forgot to come back and look at the topic. I ended up doing an end-run with this laptop. I copied the files to an external hard drive that was shared on one of the other Windows PCs, then I would run the program that needed to access that file by pointing it to the external hard drive. Actually worked out well, with only a modicum of work.
Secondly, THANK YOU for this incredibly thorough troubleshooting guide. No one else had taken the time to put something like this together for me, and I so appreciate it (more than I can convey).
And, finally, before I was even able to go through the steps you had listed, today the connection mysteriously started to work. I'm not kidding. I finished reading your post, went back to my office to log the answers to the first set of questions, and when I attempted to connect from MBP17 to Windows #4 (as we are naming them), it connected. Totally. Like I was able to copy a file without a problem.
I swear to you, I have done absolutely NOTHING to the network or computers!!
Anyway.... sorry for the long-windedness. I am going to "Evernote" this post, so that if the computer ghosts decide to mess with me again, I'll have something to throw at them.
Thank you so much!