MY Laptop wont play dvd and video files anymore after it got reformatted all i hear is audio no vid in WMP?

I reformatted my compaq presario r3000 laptop at the computer shop last few days and now when i tried playing dvd it wont play either in windows media player or Nero player... if i used windows media player it says i need to lower the color and resolution but when i lowered it its the same..when i used nero it says cant play dvd coz no dvd decoder plug-in.... i tried playing the sample windows media player video clip but all i got is sound but no vid..just black screen. My webcam works fine if use online or making video clips but it wont play in Windows media player.