playing a dvd

[eoghan]

Hi
Im trying to open a dvd and play it. I am trying a number of programs 
but I cannot seem to get it to open my dvd.
I have tried totem, kmplayer and finally mplayer from terminal.
$mplayer dvd://1
gives me:

libdvdread: Could not open device with libdvdcss.
libdvdread: Can't open /dev/acd0 for reading.
Couldn't open DVD device: /dev/acd0

This seems to have happened a few weeks ago, because i have used 
kmplayer (on gnome) before and I had no problems playing dvd's.
Could someone help me out?
Thanks
Eoghan