Thanks to a response in Howardforums, I have solved my problem.
I googled something LIKE "solving google play store problem," and that led to a useful link: I chose the most recent one, which was dated Nov. 23, 2013.
Solution was quickly achieved by following advice to..."Empty the cache." Thus, I accessed "Application Manager," selected Google Play Store, and clicked at the bottom: "Empty cache."
Perhaps this will help some other unfortunate updates to Android 4.1.3