The problem ISN'T with Flash Player. It's with IE11. Yahoo, Facebook, BBC, CBC, ESPN, NFL and NBA websites have all reported problems with IE11 specifically. The sites don't recognize the browser and therefore can't recognize the plugins in the browser. It's all in the code of IE11.
I have machines with XP, Vista, 7, 8 and 8.1 and they ALL run 11.9.900.170 with IE, Firefox, Chrome, Safari and Opera. IE11 is the only one that causes problems, on Win 7, 8 and 8.1. The other browser work fine in ALL OS builds.
Windows 98 (1st Edition), Windows ME, XP (Service Pack 1), IE7, VIsta, Windows 8... ALL have been abominable. That gives Microsoft about a .500 batting record when it comes to major new products over the last fifteen years. That's why I use Firefox on a Mac. While not everyone can afford to switch to Mac, Firefox is free, as are Chrome, Safari and Opera. Chrome isn't very popular because it's bundled with other things, and it's a resource hog, but there's nothing apart from pure stubbornness keeping people, who aren't locked down at work, from dumping Internet Exploder in favor of something that works all the time.