May never be answered, the cure is simple. Install DVD player software.
Here's one -> http://download.cnet.com/VLC-Media-Player/3000-13632_4-10267151.html
If you want what Dell supplied, check your install CDs. It is usually on the supplemental CD.
I have a Dell Deminsions 280 when I got it the DVD player worked and played DVD movies but for some reason it wont do it now say no software installed this is funny becouse nothing has been deleted from the system could you help me with this Thanks Thomas Maynard