|Most likely there is not enough voltage available at the usb ports to drive the DVD unit.|
Buying a Mains-powered USB Hub should be the answer. Plug the hub into a mains wall socket and into a USB port on your PC.
Now plug your DVD unit into the USB ports on the new hub.
Do not use the adapter that you were using earlier. Plug each usb plug on the DVD unit into a different USB port on the mains-powered hub.
Make sure the mains-powered hub you buy is actually supplied with the mains adapter as some of them can be mains-powered but you don't get the mains adapter with it.
Example of mains-powered USB hub: http://www.bestbuy.com/site/Belkin+...