Do you have a multi-channel HT setup or a 2-channel setup? It sounds like you have the DVD player set up for multi-channel output, but don't have the system (or the setup) to support it.
Almost all dialog comes from the center channel in a multi-channel setup. If you don't have center channel output and are sending Dolby Digital 5.1 or DTS from the DVD player, you will not get the dialog.
It is useless to speculate until you tell us about your system. What is the setup? 2-channel or multi-channel? What electronics and speakers are you using, etc.?
TIC
Almost all dialog comes from the center channel in a multi-channel setup. If you don't have center channel output and are sending Dolby Digital 5.1 or DTS from the DVD player, you will not get the dialog.
It is useless to speculate until you tell us about your system. What is the setup? 2-channel or multi-channel? What electronics and speakers are you using, etc.?
TIC