First make sure you have the correct video playing software for the file type. ie for a *.rm file you need real player and .avi you need windows media player. If it's an mpg, mpeg, or avi and it won't play, in my experiences around campus, most people with that problem need to download the divX codex. http://www.divx.com/download/downloadlist.php?typeid=1 . If these two quick fixes are not the problem, please send some more info so we can help you out better (like the file extension and what program you are trying to use to play it. what version of windows, macOS you use. and anything else that might help us better help you).