If you have the codecs installed and are still not to play videos in Vista or get errors like –
Media Player encountered a problem
or VLC plays only audio and not video, here is a solution for your problem (assuming you have VLC installed)-
1) Open VLC player
2) Click Settings > Preferences
3) Expand the “Video menu”
4) Highlight “Output Modules” ( by Clicking on it )
5) Located bottom right of the window, click “Advanced Options”
6) Under “Video OutPut Module” Select either one of the following options ( If one fails, try the other )
DirectX Video OutPut
Windows GDI Video OutPut (I had best luck with this)
Note that Default is usually the best option, so this is only to be changed if you have problems.
7) If these fail, you can try Dummy Video OutPut Function, or even one of the others.