Video or audio not playing ? Use VLC.

• Download VLC media player on the official VLC website :
http://www.videolan.org/vlc/
(for Windows => http://www.videolan.org/vlc/download-windows.html )

If you have an old computer, try to close running programs while playing a video.
As they are 60fps (frames per second) videos, an average/good CPU is required to play them smoothly.