Do you see the M button?
Are all the video sites that you want to use enabled?
Is the setting "enable video sites globally" enabled?
If all the above are yes try this.
past this link.
http://www.youtube.com/watch?v=GpVxsZojPUA
Highlight it and press the M button. It should wrap it in [media] tags.
submit it. What does it say?
If you're still having problems let me know and I'll take a look at it.