Windows Media Player doesn't play DVD's as far as I am aware.
Do you have any DVD Player software installed on this system? For example my laptop has Cyberlink PowerDVD 8 installed which allows me to watch DVDs.
If you don't, try the free open source VLC Player, http://www.videolan.org/vlc/
"It plays Everything!", they say.
Have a samsung external DVD writer SE S0840 for my mini 1000 HP netbook (Christmas Gift). When I try to play a DVD using Microsoft media player get message that I need a decoder. Please advised . Thanks.Squibbey