If you can't see the video (black screen), you should install or upgrade Flash Player. It's a free software easy to install, you can download it on Adobe.com.
Press the play button to launch the pre-loading of the video, then press pause to allow the video to download before watching it (progression of the gray bar). This will enable you to view the video smoothly.
Videos for downloading in .mov and .mp4 formats can be read with Quicktime Player, a software you can download for free on Apple.com.
Videos for downloading in .wmv format can be read with Windows Media Player, a software you can download for free on Microsoft.com.