MS deliberately screwed with the User-Agent strings for IE11, to 'trick websites' out of identifying it as IE (apparently they're ashamed of their latest build of their flagship browser).
Some sites ID it as Firefox, some as Safari or Opera. But, since the IE browser engine can't function with content for Gecko or Webkit, it "pooch's" the viewing of the site.
If the pages can't ID the browser, they can't ID the plug-ins in it either. This has been a major problem with Windows 8, but it's starting to pop up more and more with 7 too.
Microsoft's recommendation is to use Compatibility View for affected pages, and "pretend" you're using a different browser. Trouble with that is... it's seen limited success at best, and you have to individually enable it for EVERY page that has problems.
I'm not big on "pretending" so I recommend actually using another browser.
ANY of those will work where IE11 won't, with the Flash Player Plug-in (For all other browsers), and Chrome doesn't even need that because it has its own Flash Player plugin built in.