Dvd Audio Garbled

Question

I have an XP Compaq Presario SR1950NX AMD 64 desktop computer. I am noticing as of late that each time I try to run a dvd like a fitness dvd or a dvd movie the audio quality is HORRIBLE. I originally thought my speakers were shot and changed them 2xs this did not improve. I then tried the sound quality on audio cds and it was perfect. I need to use my fitness dvds with better quality what can I do? I do not want to use them in the tv since there is no tv where I am working out. Help!