QSI CDRW/DVD SWB-242U Sound Problem

Funny enough, after installing the driver for the QSI CDRW/DVD SWB-242U drive, the following happens:

I can play any audio CD, DVD with MP3 or data CD and the sound works fine, however when I try to play DVDs (movies, etc...) there is no sound. The movie plays fine but I cannot hear anything. I've cheked all soundcard settings and no luck. I use Windows Media Player to play DVDs and audio CDs. Any suggestions anyone?

Much appreciated.