can't play dvd's

i just bought a powerbook (hooray!) but sadly i can't seem to play a dvd on it (boo).

So I've tried three different dvd's that work in my dvd player and on my pc. all bought through amazon.

i put them into my powerbook, the DVD Player starts up (no icon on my desktop), but the DVD Player just sits there with a black screen. I hit the 'Play' button on the dvd player and on the screen comes up the words 'Disc not available'

what is going wrong here? any ideas/advice?

thanks
tyler

 

i should mention that i am, in fact, able to put in cd's to install software, included the OS discs 1 and two that came with my powerbook. I'm pretty sure these are DVD's... so perhaps just movie dvd's?