No Sound when I play a DVD, but I do have sound... Just purchased a internal Liteon 20x DVD/CD

Question

Just purchased a internal Liteon 20x DVD/CD Writer & re writer. when I play a dvd I have the picture but not the sound, but when I play a Music CD I hear the audio. My desktop is a Compaq Presario S3060AN..I followed installation instuctions..Please help I 'm at my wits end. It does burn photo's etc to CD - DVD writer came witn Nero

I have Compaq Presario F500. When I put DVD in picture but no sound. But if I copy it in to a computer sound work. I make copy of DVD. It work find on DVD player. Is it a problem with computer or program.