I have some questions to help fix it LS.
First of all when you say it isn't playing anything but sound what are you using to play it on your PC?
It sounds like you just don't have Flash installed or it needs updated but depending on how the video was made and what you are using to play it could be something else.
The first thing I would try would be to make sure you have Flash installed.
Adobe - Install Adobe Flash Player
Let me know if that doesn't work.