Class not registered

[Thomas]

Hi,

My girl friend trys to play DVD on her PC. The Window
Media Player did open the playlist, but was unable to
play the DVD, saying " General error, Class not
Registered." Then after she clicked on help, the
following appeared: "You have encountered the following
error while using Windows Media Player: Error# 80040154
Sorry, no more help is available for this problem at this
time."

Can someone help me?

Thanks a lot.

Thomas