DVDs wont play in WMP or Media Centre

In media centre if i try to play a dvd it says:

Cannot Play DVD
The DVD may be in use by another program ((there are no other programs running)). If all other applications are closed the display resolution may need to be lowered or the display connection type may not support the playback of the DVD.

Lowering the resolution does not help.
I have a MSI 7900gto graphics card. I have tried downloading numerous codecs, including the nvidia one you have to pay for. No success... I also have the latest nvidia drivers for my gpu.
The dvd does work in VLC, but anything works in VLC, and i would prefer to use Media Centre in conjunction with the remote.

And, in windows media player, it shows that something is playing, and it can see that it is a family guy dvd, and it even has the picture, but there is no video and no audio.

Any help greatly appreciated as usual.