I purchased a refurbished XPS M1330 with Vista Office on it.  Tot Mem 895 MB,  Gen PnP Monitor on NVIDIA GeForce 8400M GS.  I have installed the Roxio Creator & My DVD 9.0 DE that cme with the Laptop.  I canot currently play a DVD, the message that comes up says that "Windows Media cannot play the DVD because a compatible DVD decoder is not installed on your computer"

The Laptop was able to play a DVD when I received it, so where did it go, I did not get a separate disc for it.  Does anyone know how I can get it back?