The first thing I would try is a Flash Player update. You can go to the Adobe website and download/install it for free.
If it says you have the most current version then you can try to uninstall Flash Player using the Flash Player Removal Tool and then reinstall it from the website. You may actually want to try to uninstall it first even before trying to see if you have the most current version.
Also make sure you have an adequate internet connection to play streaming videos. If you are on a dial up or very slow broadband connection then that may be the cause. You can use a site such as Speedtest.net to run a test. But with today's fast connections that shouldn't really be a problem unless you are using a cellular hotspot.
Another option is to check and see if its a web browser issue. If you are using Internet Explorer for example then try out Firefox and see if that fixes it. You can have both IE and Firefox installed at the same time.You might want to run the Flash Player update again after installing Firefox.