In this article - in detail about the possible reasons why video is not shown in classmates and how to eliminate these reasons to correct the problem.
Browser is outdated?
If you have never even tried to watch video in classmates through the used browser, then the option is quite possible that you have an outdated browser. Perhaps this is in other cases. Upgrade it to the latest version of the developer version available on the official website. Or, if you do not bother the transition to a new browser - I would recommend using Google Chrome. Although, in fact, Opera is now moving to technologies that are used in existing CHROME versions (WebKit. In turn, Chrome goes to a new engine).Perhaps in this regard will be useful: the best browser for Windows will be useful.
Adobe Flash Player.
Regardless of what your browser you have, download from the official site and install the plugin to play Flash. To do this, follow the link http://get.adobe.com/ru/flashplayer/. In case you have a Google Chrome (or another browser with built-in flash playing), then instead of the plug-in page of the plug-in, you will see a message that the plugin is not needed for your browser.
Load the plugin and install. After that, close and open the browser again. Go to classmates and see if video earned. However, it may not help, read further.
Content Lock Extensions
If your browser has any extensions for blocking advertising, JavaScript, cookies, then all of them may cause the video in classmates. Try to turn off these extensions and check whether the problem was solved.Quick Time.
If you are using Mozilla Firefox, download and install the QuickTime plugin from the Apple official site http://www.apple.com/quicktime/download/. After installation, this plugin will be available not only in Firefox, but also in other browsers and programs. Perhaps this will solve the problem.
Drivers for video cards and codecs
If you do not play a video in classmates, it may well be that you do not have the desired drivers for the video card. It is especially likely if you do not play modern games. With simple work, the lack of native drivers can be invisible. Download and install the latest drivers for your video card from the video card manufacturer. Restart the computer and check whether the video opens in classmates.
Just in case, update (or install) codecs on the computer - set, for example, K-Lite Codec Pack.
And one more theoretically possible reason: malicious programs. If there is a suspicion for the presence of those, I recommend checking the test using the ADWCleaner.