I have installed a new LiteOn Model LH-18A1P186C  DVD Writer in my computer.
After INSTALLATION I can play Audio CDs , write to blank CDs but when viewing
DVDs cannot hear any sound. Any HELP appreciated

WIN XP SP2, 512Mb RAM 40G HDWhat are you using to play the DVDs?
You need some sort of codec or DVD playing program.
Are you sure the sound isn't muted or turned down?
Does this happen with all DVDs?Double-check all your settings in Control Panel/Sounds and Multimedia...All of the settings in Sounds/Audio in the control panel APPEAR to be correct, nothing is muted.

When I insert the DVD for playing, I am given the option to play the DVD with Windows Media Player.
I have never tried viewing a DVD in this manner.

 Is a separate software program or codec required?

I thought it unusual that I have sound for my music CDs but not for the DVDs.

Yes, it happens on all DVDs.

ThanksYou can get just what you need here to use media player:

http://www.theorica.net/download.htm

Choose this one near the bottom of the page:

The Codecs 5.0 - 9x/ME/2000/XP (English)

You can also use VLC player, which is free here:

http://www.videolan.org/Thanks to all for your help!

The codecs download from Theorica.net did the job.
I now  have picture and sound from my DVDs.Glad you are all FIXED up and thanks for posting back.